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AP Calculus BC Quiz

AP Calculus BC Quiz: Differentiating Inverse Trigonometric Functions

Practice Differentiating Inverse Trigonometric Functions in AP Calculus BC with focused quiz questions that help you check what you know, review explanations, and build confidence with test-style prompts.

Question 1 / 20

0 of 20 answered

A navigation algorithm uses p(x)=\arcsec(4x)p(x)=\arcsec(4x)p(x)=\arcsec(4x). What is p′(x)p'(x)p′(x) for x≠0x\neq 0x=0?

Select an answer to continue

What this quiz covers

This quiz focuses on Differentiating Inverse Trigonometric Functions, giving you a quick way to practice the rules, question types, and explanations that matter most for AP Calculus BC.

How to use this quiz

Try each quiz question before looking at the correct answer. Use the explanations to review missed ideas, then come back to similar questions until the pattern feels familiar.

All questions

Question 1

A navigation algorithm uses p(x)=\arcsec(4x)p(x)=\arcsec(4x)p(x)=\arcsec(4x). What is p′(x)p'(x)p′(x) for x≠0x\neq 0x=0?

  1. 41−16x2\dfrac{4}{\sqrt{1-16x^2}}1−16x2​4​
  2. 41+16x2\dfrac{4}{\sqrt{1+16x^2}}1+16x2​4​
  3. 4∣4x∣16x2−1\dfrac{4}{|4x|\sqrt{16x^2-1}}∣4x∣16x2−1​4​ (correct answer)
  4. 11+16x2\dfrac{1}{1+16x^2}1+16x21​
  5. −41−16x2\dfrac{-4}{\sqrt{1-16x^2}}1−16x2​−4​

Explanation: Differentiating inverse trigonometric functions is the key skill here, specifically finding the derivative of arcsec(4x). The formula for the derivative of arcsec(u) where u is a function of x is (1 / (|u| sqrt(u^2 - 1))) times u'. In this case, u = 4x, so u' = 4, leading to p'(x) = 4 / (|4x| sqrt((4x)^2 - 1)). Simplifying, that's 4 / (|4x| sqrt(16x^2 - 1)), which matches choice C. A tempting distractor like choice E fails because it includes a negative sign and uses the wrong form without the absolute value and square root of u^2 - 1. Always remember to apply the chain rule when differentiating composite inverse trig functions and double-check the sign based on the specific function.

Question 2

A sensor records g(t)=arctan⁡(5t−1)g(t)=\arctan(5t-1)g(t)=arctan(5t−1). What is g′(t)g'(t)g′(t)?

  1. 11−(5t−1)2\dfrac{1}{\sqrt{1-(5t-1)^2}}1−(5t−1)2​1​
  2. 51+(5t−1)2\dfrac{5}{1+(5t-1)^2}1+(5t−1)25​ (correct answer)
  3. 51−(5t−1)2\dfrac{5}{\sqrt{1-(5t-1)^2}}1−(5t−1)2​5​
  4. 11+(5t−1)2\dfrac{1}{1+(5t-1)^2}1+(5t−1)21​
  5. −51+(5t−1)2\dfrac{-5}{1+(5t-1)^2}1+(5t−1)2−5​

Explanation: This problem involves differentiating the inverse tangent function with a linear argument. The derivative of arctan(u) is 1/(1+u²) · u', where u = 5t-1. Using the chain rule, we have d/dt[arctan(5t-1)] = 1/(1+(5t-1)²) · d/dt[5t-1] = 1/(1+(5t-1)²) · 5 = 5/(1+(5t-1)²). Choice D incorrectly forgets to multiply by the derivative of the inner function (which is 5). For inverse trig derivatives, the chain rule factor from the inner function's derivative is essential.

Question 3

For a model of tilt angle, p(x)=\arcsec(4x)p(x)=\arcsec(4x)p(x)=\arcsec(4x). What is p′(x)p'(x)p′(x)?

  1. 41−(4x)2\dfrac{4}{\sqrt{1-(4x)^2}}1−(4x)2​4​
  2. 41+(4x)2\dfrac{4}{1+(4x)^2}1+(4x)24​
  3. 1∣4x∣(4x)2−1\dfrac{1}{|4x|\sqrt{(4x)^2-1}}∣4x∣(4x)2−1​1​
  4. 4∣4x∣(4x)2−1\dfrac{4}{|4x|\sqrt{(4x)^2-1}}∣4x∣(4x)2−1​4​ (correct answer)
  5. −4∣4x∣(4x)2−1\dfrac{-4}{|4x|\sqrt{(4x)^2-1}}∣4x∣(4x)2−1​−4​

Explanation: This problem involves differentiating the inverse secant function. The derivative of arcsec(u) is 1/(|u|√(u²-1)) · u', where u = 4x. Using the chain rule, we get d/dx[arcsec(4x)] = 1/(|4x|√((4x)²-1)) · d/dx[4x] = 1/(|4x|√(16x²-1)) · 4 = 4/(|4x|√(16x²-1)). Note that (4x)² = 16x², so √((4x)²-1) = √(16x²-1). Choice C incorrectly omits the chain rule factor of 4. For arcsec and arccsc, remember both the absolute value in the denominator and the chain rule multiplication.

Question 4

A navigation routine uses u(x)=arccsc⁡(x2+3)u(x)=\operatorname{arccsc}(x^2+3)u(x)=arccsc(x2+3). What is u′(x)u'(x)u′(x)?

  1. 2x1−(x2+3)2\dfrac{2x}{\sqrt{1-(x^2+3)^2}}1−(x2+3)2​2x​
  2. −2x1+(x2+3)2-\dfrac{2x}{1+(x^2+3)^2}−1+(x2+3)22x​
  3. −2x∣x2+3∣(x2+3)2−1-\dfrac{2x}{|x^2+3|\sqrt{(x^2+3)^2-1}}−∣x2+3∣(x2+3)2−1​2x​ (correct answer)
  4. 2x∣x2+3∣(x2+3)2−1\dfrac{2x}{|x^2+3|\sqrt{(x^2+3)^2-1}}∣x2+3∣(x2+3)2−1​2x​
  5. −2x(x2+3)2−1-\dfrac{2x}{\sqrt{(x^2+3)^2-1}}−(x2+3)2−1​2x​

Explanation: This problem requires differentiating arccsc, another less common inverse trig function. The derivative of arccsc(u) is -u'/(|u|√(u²-1)), where u = x² + 3. Using the chain rule, u' = 2x. Therefore, u'(x) = -2x/(|x²+3|√((x²+3)²-1)), which is choice C. Choice D omits the negative sign essential for arccsc. Choice E lacks the absolute value term. Remember that arccsc, like arccos and arccot, includes a negative sign in its derivative.

Question 5

A geometry algorithm uses q(x)=\arccot(x3)q(x)=\arccot(x^3)q(x)=\arccot(x3). What is q′(x)q'(x)q′(x)?

  1. 3x21+x6\dfrac{3x^2}{1+x^6}1+x63x2​
  2. −3x21+x6-\dfrac{3x^2}{1+x^6}−1+x63x2​ (correct answer)
  3. 3x21−x6\dfrac{3x^2}{\sqrt{1-x^6}}1−x6​3x2​
  4. −3x21−x6-\dfrac{3x^2}{\sqrt{1-x^6}}−1−x6​3x2​
  5. 3x2∣x3∣x6−1\dfrac{3x^2}{|x^3|\sqrt{x^6-1}}∣x3∣x6−1​3x2​

Explanation: This problem requires differentiating arccot with a power function argument. The derivative of arccot(u) is -u'/(1+u²), where u = x³. Using the power rule, u' = 3x². Therefore, q'(x) = -3x²/(1+x⁶), which matches choice B. Choice A omits the negative sign essential for arccot. Choice D incorrectly uses the arccos formula with √(1-u²). Remember that arccot, like arccos, includes a negative sign in its derivative formula.

Question 6

For a signal phase shift, p(x)=arcsec⁡(2x+1)p(x)=\operatorname{arcsec}(2x+1)p(x)=arcsec(2x+1). What is p′(x)p'(x)p′(x)?

  1. 21−(2x+1)2\dfrac{2}{\sqrt{1-(2x+1)^2}}1−(2x+1)2​2​
  2. 21+(2x+1)2\dfrac{2}{1+(2x+1)^2}1+(2x+1)22​
  3. 2∣2x+1∣(2x+1)2−1\dfrac{2}{|2x+1|\sqrt{(2x+1)^2-1}}∣2x+1∣(2x+1)2−1​2​ (correct answer)
  4. −21−(2x+1)2-\dfrac{2}{\sqrt{1-(2x+1)^2}}−1−(2x+1)2​2​
  5. 2(2x+1)2−1\dfrac{2}{\sqrt{(2x+1)^2-1}}(2x+1)2−1​2​

Explanation: This problem involves differentiating arcsec, one of the less common inverse trig functions. The derivative of arcsec(u) is u'/(|u|√(u²-1)), where u = 2x + 1. Using the chain rule, u' = 2. Therefore, p'(x) = 2/(|2x+1|√((2x+1)²-1)), which is choice C. Choice A incorrectly uses the arcsin formula, while choice E omits the absolute value. For arcsec and arccsc, always include |u| in the denominator along with √(u²-1).

Question 7

A robot’s turning angle is r(s)=arccos⁡(1−4s)r(s)=\arccos(1-4s)r(s)=arccos(1−4s). What is r′(s)r'(s)r′(s)?

  1. 41−(1−4s)2\dfrac{4}{\sqrt{1-(1-4s)^2}}1−(1−4s)2​4​ (correct answer)
  2. −41−(1−4s)2-\dfrac{4}{\sqrt{1-(1-4s)^2}}−1−(1−4s)2​4​
  3. −41−(1−4s)2\dfrac{-4}{\sqrt{1-(1-4s)^2}}1−(1−4s)2​−4​
  4. 41+(1−4s)2\dfrac{4}{1+(1-4s)^2}1+(1−4s)24​
  5. 41+(1−4s)2\dfrac{4}{\sqrt{1+(1-4s)^2}}1+(1−4s)2​4​

Explanation: This problem involves differentiating arccos with a linear composite function. The derivative of arccos(u) is -1/√(1-u²), and we apply the chain rule with u = 1-4s. Differentiating: r'(s) = -1/√(1-(1-4s)²) · d/ds(1-4s) = -1/√(1-(1-4s)²) · (-4) = 4/√(1-(1-4s)²). The two negative signs cancel to give a positive result. Choice B incorrectly keeps the negative sign as -4/√(1-(1-4s)²). For inverse trig derivatives, carefully track signs when both arccos (negative derivative) and decreasing inner functions are involved.

Question 8

A ramp angle satisfies p(u)=arctan⁡(u3)p(u)=\arctan(u^3)p(u)=arctan(u3). What is p′(u)p'(u)p′(u)?

  1. 3u21+(u3)2\dfrac{3u^2}{\sqrt{1+(u^3)^2}}1+(u3)2​3u2​
  2. 3u21+(u3)2\dfrac{3u^2}{1+(u^3)^2}1+(u3)23u2​ (correct answer)
  3. 3u21−(u3)2\dfrac{3u^2}{\sqrt{1-(u^3)^2}}1−(u3)2​3u2​
  4. −3u21−(u3)2-\dfrac{3u^2}{\sqrt{1-(u^3)^2}}−1−(u3)2​3u2​
  5. −3u21+(u3)2-\dfrac{3u^2}{1+(u^3)^2}−1+(u3)23u2​

Explanation: This problem involves differentiating arctangent with a cubic composite function. The derivative of arctan(u) is 1/(1+u²), without any square root, and we apply the chain rule with u = u³. Differentiating: p'(u) = 1/(1+(u³)²) · d/du(u³) = 1/(1+u⁶) · 3u² = 3u²/(1+u⁶). Choice C incorrectly uses the arcsin derivative formula with 1-u² under a square root, giving 3u²/√(1-(u³)²). For inverse trig derivatives, arctangent is unique in having no square root and using 1+u² rather than 1-u² in the denominator.

Question 9

In an experiment, r(x)=arcsin⁡ ⁣(x2)r(x)=\arcsin\!\left(\dfrac{x}{2}\right)r(x)=arcsin(2x​). What is r′(x)r'(x)r′(x)?

  1. 11−(x2)2\dfrac{1}{\sqrt{1-\left(\frac{x}{2}\right)^2}}1−(2x​)2​1​
  2. 121−(x2)2\dfrac{1}{2\sqrt{1-\left(\frac{x}{2}\right)^2}}21−(2x​)2​1​ (correct answer)
  3. −121−(x2)2-\dfrac{1}{2\sqrt{1-\left(\frac{x}{2}\right)^2}}−21−(2x​)2​1​
  4. 12(1+(x2)2)\dfrac{1}{2\left(1+\left(\frac{x}{2}\right)^2\right)}2(1+(2x​)2)1​
  5. −11−(x2)2-\dfrac{1}{\sqrt{1-\left(\frac{x}{2}\right)^2}}−1−(2x​)2​1​

Explanation: This problem involves differentiating the inverse sine function, a key skill in AP Calculus BC. The derivative formula for arcsin(u) is u' divided by the square root of 1 minus u squared. Here, u equals x over 2, so u' is 1 over 2. Applying the formula gives (1 over 2) over the square root of 1 minus (x over 2) squared, which is 1 over (2 times the square root of 1 minus (x over 2) squared). A tempting distractor is choice A, which forgets the chain rule factor of 1 over 2 from u'. Always remember to apply the chain rule correctly and verify the sign based on the specific inverse trig function's derivative formula.

Question 10

A sensor outputs f(x)=arcsin⁡(3x2)f(x)=\arcsin(3x^2)f(x)=arcsin(3x2). What is f′(x)f'(x)f′(x) for values of xxx where defined?

  1. 6x1−9x4\dfrac{6x}{\sqrt{1-9x^4}}1−9x4​6x​ (correct answer)
  2. 6x1+9x4\dfrac{6x}{1+9x^4}1+9x46x​
  3. −6x1−9x4-\dfrac{6x}{\sqrt{1-9x^4}}−1−9x4​6x​
  4. 6x1+9x4\dfrac{6x}{\sqrt{1+9x^4}}1+9x4​6x​
  5. −6x1+9x4-\dfrac{6x}{1+9x^4}−1+9x46x​

Explanation: This problem involves differentiating the inverse sine function, a key skill in AP Calculus BC. The derivative formula for arcsin(u) is u' divided by the square root of 1 minus u squared. Here, u equals 3x squared, so u' is 6x. Applying the formula gives 6x over the square root of 1 minus (3x squared) squared, which simplifies to 6x over the square root of 1 minus 9x to the fourth. A tempting distractor is choice C, which includes a negative sign, but that would be incorrect because the arcsin derivative formula does not inherently include a negative unlike arccos. Always remember to apply the chain rule correctly and verify the sign based on the specific inverse trig function's derivative formula.

Question 11

In a model, g(x)=arctan⁡(5x−1)g(x)=\arctan(5x-1)g(x)=arctan(5x−1). What is g′(x)g'(x)g′(x)?

  1. 51−(5x−1)2\dfrac{5}{\sqrt{1-(5x-1)^2}}1−(5x−1)2​5​
  2. 51+(5x−1)2\dfrac{5}{1+(5x-1)^2}1+(5x−1)25​ (correct answer)
  3. 51+(5x−1)2\dfrac{5}{\sqrt{1+(5x-1)^2}}1+(5x−1)2​5​
  4. −51+(5x−1)2-\dfrac{5}{1+(5x-1)^2}−1+(5x−1)25​
  5. 51−(5x−1)2\dfrac{5}{1-(5x-1)^2}1−(5x−1)25​

Explanation: This problem involves differentiating the inverse tangent function, a key skill in AP Calculus BC. The derivative formula for arctan(u) is u' divided by 1 plus u squared. Here, u equals 5x minus 1, so u' is 5. Applying the formula gives 5 over 1 plus (5x minus 1) squared. A tempting distractor is choice A, which uses the arcsin formula with a square root instead of the correct arctan denominator. Always remember to apply the chain rule correctly and verify the sign based on the specific inverse trig function's derivative formula.

Question 12

A controller uses h(x)=arccos⁡(2x)h(x)=\arccos(2x)h(x)=arccos(2x). What is h′(x)h'(x)h′(x)?

  1. 21−4x2\dfrac{2}{\sqrt{1-4x^2}}1−4x2​2​
  2. −21−4x2-\dfrac{2}{\sqrt{1-4x^2}}−1−4x2​2​ (correct answer)
  3. 21+4x2\dfrac{2}{1+4x^2}1+4x22​
  4. −21+4x2-\dfrac{2}{1+4x^2}−1+4x22​
  5. −21+4x2-\dfrac{2}{\sqrt{1+4x^2}}−1+4x2​2​

Explanation: This problem involves differentiating the inverse cosine function, a key skill in AP Calculus BC. The derivative formula for arccos(u)arccos(u)arccos(u) is negative u′u'u′ divided by the square root of 1−u21 - u^21−u2. Here, u equals 2x, so u′u'u′ is 2. Applying the formula gives negative 2 over the square root of 1−(2x)21 - (2x)^21−(2x)2, which is negative 2 over the square root of 1−4x21 - 4x^21−4x2. A tempting distractor is choice A, which omits the negative sign inherent to the arccos derivative. Always remember to apply the chain rule correctly and verify the sign based on the specific inverse trig function's derivative formula.

Question 13

A calibration curve is t(x)=arccos⁡(x2)t(x)=\arccos(x^2)t(x)=arccos(x2). What is t′(x)t'(x)t′(x) for ∣x∣<1|x|<1∣x∣<1?

  1. 2x1−x4\dfrac{2x}{\sqrt{1-x^4}}1−x4​2x​
  2. −2x1−x4\dfrac{-2x}{\sqrt{1-x^4}}1−x4​−2x​ (correct answer)
  3. 2x1+x4\dfrac{2x}{1+x^4}1+x42x​
  4. −2x1+x4\dfrac{-2x}{1+x^4}1+x4−2x​
  5. −2x1+x4\dfrac{-2x}{\sqrt{1+x^4}}1+x4​−2x​

Explanation: Differentiating inverse trigonometric functions is the key skill here, specifically finding the derivative of arccos(x^2). The formula for the derivative of arccos(u) where u is a function of x is (-1 / sqrt(1 - u^2)) times u'. In this case, u = x^2, so u' = 2x, leading to t'(x) = -2x / sqrt(1 - (x^2)^2). Simplifying, that's -2x / sqrt(1 - x^4), which matches choice B. A tempting distractor like choice A fails because it omits the negative sign specific to arccos. Always remember to apply the chain rule when differentiating composite inverse trig functions and double-check the sign based on the specific function.

Question 14

A signal phase shift is q(x)=\arccsc(x3)q(x)=\arccsc(x^3)q(x)=\arccsc(x3). What is q′(x)q'(x)q′(x) for x≠0x\neq 0x=0?

  1. −3x2∣x3∣x6−1\dfrac{-3x^2}{|x^3|\sqrt{x^6-1}}∣x3∣x6−1​−3x2​ (correct answer)
  2. 3x2∣x3∣x6−1\dfrac{3x^2}{|x^3|\sqrt{x^6-1}}∣x3∣x6−1​3x2​
  3. −3x21−x6\dfrac{-3x^2}{\sqrt{1-x^6}}1−x6​−3x2​
  4. 3x21+x6\dfrac{3x^2}{1+x^6}1+x63x2​
  5. −3x21+x6\dfrac{-3x^2}{\sqrt{1+x^6}}1+x6​−3x2​

Explanation: Differentiating inverse trigonometric functions is the key skill here, specifically finding the derivative of arccsc(x^3). The formula for the derivative of arccsc(u) where u is a function of x is (-1 / (|u| sqrt(u^2 - 1))) times u'. In this case, u = x^3, so u' = 3x^2, leading to q'(x) = -3x^2 / (|x^3| sqrt((x^3)^2 - 1)). Simplifying, that's -3x^2 / (|x^3| sqrt(x^6 - 1)), which matches choice A. A tempting distractor like choice B fails because it omits the negative sign essential to the arccsc derivative. Always remember to apply the chain rule when differentiating composite inverse trig functions and double-check the sign based on the specific function.

Question 15

A sensor model uses f(x)=arcsin⁡(3x)f(x)=\arcsin(3x)f(x)=arcsin(3x) for ∣x∣<13|x|<\tfrac13∣x∣<31​. What is f′(x)f'(x)f′(x)?

  1. 31−9x2\dfrac{3}{\sqrt{1-9x^2}}1−9x2​3​ (correct answer)
  2. 31+9x2\dfrac{3}{\sqrt{1+9x^2}}1+9x2​3​
  3. −31−9x2\dfrac{-3}{\sqrt{1-9x^2}}1−9x2​−3​
  4. 11+9x2\dfrac{1}{1+9x^2}1+9x21​
  5. 11−9x2\dfrac{1}{1-9x^2}1−9x21​

Explanation: Differentiating inverse trigonometric functions is the key skill here, specifically finding the derivative of arcsin(3x). The formula for the derivative of arcsin(u) where u is a function of x is (1 / sqrt(1 - u^2)) times u'. In this case, u = 3x, so u' = 3, leading to f'(x) = 3 / sqrt(1 - (3x)^2). Simplifying, that's 3 / sqrt(1 - 9x^2), which matches choice A. A tempting distractor like choice C fails because it includes a negative sign, which would apply to arccos but not arcsin. Always remember to apply the chain rule when differentiating composite inverse trig functions and double-check the sign based on the specific function.

Question 16

A medical device models response as v(x)=\arccsc(2x2+1)v(x)=\arccsc(2x^2+1)v(x)=\arccsc(2x2+1). What is v′(x)v'(x)v′(x)?

  1. 4x1−(2x2+1)2\dfrac{4x}{\sqrt{1-(2x^2+1)^2}}1−(2x2+1)2​4x​
  2. −4x∣2x2+1∣(2x2+1)2−1\dfrac{-4x}{|2x^2+1|\sqrt{(2x^2+1)^2-1}}∣2x2+1∣(2x2+1)2−1​−4x​ (correct answer)
  3. 4x1+(2x2+1)2\dfrac{4x}{1+(2x^2+1)^2}1+(2x2+1)24x​
  4. 4x∣2x2+1∣(2x2+1)2−1\dfrac{4x}{|2x^2+1|\sqrt{(2x^2+1)^2-1}}∣2x2+1∣(2x2+1)2−1​4x​
  5. −4x1−(2x2+1)2\dfrac{-4x}{\sqrt{1-(2x^2+1)^2}}1−(2x2+1)2​−4x​

Explanation: This problem involves differentiating the inverse cosecant function with a quadratic argument. The derivative of arccsc(u) is -1/(|u|√(u²-1)) · u', where u = 2x²+1. Using the chain rule, we have d/dx[arccsc(2x²+1)] = -1/(|2x²+1|√((2x²+1)²-1)) · d/dx[2x²+1] = -1/(|2x²+1|√((2x²+1)²-1)) · 4x = -4x/(|2x²+1|√((2x²+1)²-1)). Choice D incorrectly omits the negative sign that characterizes arccsc derivatives. For successful inverse trig differentiation, memorize which functions have negative derivatives (arccos, arccot, arccsc) versus positive ones.

Question 17

In a geometry simulation, u(x)=\arcsec(1−3x)u(x)=\arcsec(1-3x)u(x)=\arcsec(1−3x). What is u′(x)u'(x)u′(x)?

  1. −31+(1−3x)2\dfrac{-3}{1+(1-3x)^2}1+(1−3x)2−3​
  2. −31−(1−3x)2\dfrac{-3}{\sqrt{1-(1-3x)^2}}1−(1−3x)2​−3​
  3. −3∣1−3x∣(1−3x)2−1\dfrac{-3}{|1-3x|\sqrt{(1-3x)^2-1}}∣1−3x∣(1−3x)2−1​−3​ (correct answer)
  4. 3∣1−3x∣(1−3x)2−1\dfrac{3}{|1-3x|\sqrt{(1-3x)^2-1}}∣1−3x∣(1−3x)2−1​3​
  5. 1∣1−3x∣(1−3x)2−1\dfrac{1}{|1-3x|\sqrt{(1-3x)^2-1}}∣1−3x∣(1−3x)2−1​1​

Explanation: This question requires differentiating the inverse secant function with a linear argument. The derivative of arcsec(u) is 1∣u∣u2−1⋅u′\frac{1}{|u| \sqrt{u^2 - 1}} \cdot u'∣u∣u2−1​1​⋅u′, where u=1−3xu = 1 - 3xu=1−3x. Applying the chain rule gives ddx[\arcsec(1−3x)]=1∣1−3x∣(1−3x)2−1⋅ddx[1−3x]=1∣1−3x∣(1−3x)2−1⋅(−3)=−3∣1−3x∣(1−3x)2−1\frac{d}{dx} [\arcsec(1-3x)] = \frac{1}{|1-3x| \sqrt{(1-3x)^2 - 1}} \cdot \frac{d}{dx}[1-3x] = \frac{1}{|1-3x| \sqrt{(1-3x)^2 - 1}} \cdot (-3) = \frac{-3}{|1-3x| \sqrt{(1-3x)^2 - 1}}dxd​[\arcsec(1−3x)]=∣1−3x∣(1−3x)2−1​1​⋅dxd​[1−3x]=∣1−3x∣(1−3x)2−1​1​⋅(−3)=∣1−3x∣(1−3x)2−1​−3​. Choice D incorrectly uses +3 instead of -3 from the derivative of 1-3x. When differentiating inverse trig functions, pay careful attention to the sign of the inner function's derivative.

Question 18

A sound wave model uses r(x)=arcsin⁡ ⁣(x2)r(x)=\arcsin\!\left(\dfrac{x}{2}\right)r(x)=arcsin(2x​). What is r′(x)r'(x)r′(x)?

  1. 11−(x/2)2\dfrac{1}{\sqrt{1-(x/2)^2}}1−(x/2)2​1​
  2. 11+(x/2)2\dfrac{1}{1+(x/2)^2}1+(x/2)21​
  3. 121−(x/2)2\dfrac{1}{2\sqrt{1-(x/2)^2}}21−(x/2)2​1​ (correct answer)
  4. 12(1+(x/2)2)\dfrac{1}{2\left(1+(x/2)^2\right)}2(1+(x/2)2)1​
  5. −121−(x/2)2\dfrac{-1}{2\sqrt{1-(x/2)^2}}21−(x/2)2​−1​

Explanation: This problem involves differentiating arcsin with a fractional argument. The derivative of arcsin(u) is 1/√(1-u²) · u', where u = x/2. Using the chain rule, we have d/dx[arcsin(x/2)] = 1/√(1-(x/2)²) · d/dx[x/2] = 1/√(1-x²/4) · (1/2) = 1/(2√(1-x²/4)). Since √(1-x²/4) = √(1-(x/2)²), the answer is 1/(2√(1-(x/2)²)). Choice A incorrectly forgets to multiply by 1/2 from differentiating x/2. When the inner function involves fractions or division, don't forget its derivative contributes to the final answer.

Question 19

A response model is u(x)=\arccot(7x)u(x)=\arccot(7x)u(x)=\arccot(7x). What is u′(x)u'(x)u′(x)?

  1. 71+49x2\dfrac{7}{1+49x^2}1+49x27​
  2. −71+49x2\dfrac{-7}{1+49x^2}1+49x2−7​ (correct answer)
  3. 71−49x2\dfrac{7}{\sqrt{1-49x^2}}1−49x2​7​
  4. −71−49x2\dfrac{-7}{\sqrt{1-49x^2}}1−49x2​−7​
  5. 11+49x2\dfrac{1}{1+49x^2}1+49x21​

Explanation: Differentiating inverse trigonometric functions is the key skill here, specifically finding the derivative of arccot(7x). The formula for the derivative of arccot(u) where u is a function of x is (-1 / (1 + u^2)) times u'. In this case, u = 7x, so u' = 7, leading to u'(x) = -7 / (1 + (7x)^2). Simplifying, that's -7 / (1 + 49x^2), which matches choice B. A tempting distractor like choice A fails because it lacks the negative sign inherent to arccot. Always remember to apply the chain rule when differentiating composite inverse trig functions and double-check the sign based on the specific function.

Question 20

A glide path is modeled by w(x)=arccos⁡(x2−1)w(x)=\arccos(x^2-1)w(x)=arccos(x2−1). What is w′(x)w'(x)w′(x)?

  1. 2x1−(x2−1)2\dfrac{2x}{\sqrt{1-(x^2-1)^2}}1−(x2−1)2​2x​
  2. −2x1−(x2−1)2-\dfrac{2x}{\sqrt{1-(x^2-1)^2}}−1−(x2−1)2​2x​ (correct answer)
  3. 2x1+(x2−1)2\dfrac{2x}{\sqrt{1+(x^2-1)^2}}1+(x2−1)2​2x​
  4. 2x1+(x2−1)2\dfrac{2x}{1+(x^2-1)^2}1+(x2−1)22x​
  5. −2x1+(x2−1)2-\dfrac{2x}{1+(x^2-1)^2}−1+(x2−1)22x​

Explanation: This problem requires differentiating arccos with a quadratic composite function. The derivative of arccos(u) is -1/√(1-u²), and we need the chain rule with u = x²-1. Differentiating: w'(x) = -1/√(1-(x²-1)²) · d/dx(x²-1) = -1/√(1-(x²-1)²) · 2x = -2x/√(1-(x²-1)²). Choice A incorrectly omits the negative sign from the arccos derivative, giving 2x/√(1-(x²-1)²). When differentiating inverse trig functions, arccos uniquely includes a negative sign that must not be forgotten.