Calculating Higher-Order Derivatives

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AP Calculus AB › Calculating Higher-Order Derivatives

Questions 1 - 10
1

For $f(x)=\sqrt{1+x}= (1+x)^{1/2}$, what is $f''(x)$?

$f''(x)=rac{1}{4}(1+x)^{-3/2}$

$f''(x)=-rac{1}{4}(1+x)^{-3/2}$

$f''(x)=rac{1}{2}(1+x)^{-1/2}$

$f''(x)=-rac{1}{2}(1+x)^{-1/2}$

$f''(x)=-rac{3}{4}(1+x)^{-5/2}$

Explanation

Binomial roots differentiate with fractional exponents. The first is f'(x) = (1/2)(1 + $x)^{-1/2}$. The second is f''(x) = - (1/4)(1 + $x)^{-3/2}$, reducing exponent. A common error is stopping early or fraction mistakes. Chain rule applies each time. For roots, convert to exponents and differentiate iteratively, updating coefficients.

2

Let $y=xe^{-x}$. What is the second derivative $y''$?

$y''=e^{-x}(x-2)$

$y''=e^{-x}(x+2)$

$y''=e^{-x}(1-x)$

$y''=-e^{-x}(x-2)$

$y''=-e^{-x}(1-x)$

Explanation

Product of x and exponential uses product rule. The first is y' = $e^{-x}$(1 - x). The second is y'' = $e^{-x}$(x - 2), factoring properly. A common error is stopping at first or sign errors in exponential. Each differentiation involves both product and chain. For such products, apply rules successively, factoring the exponential out.

3

A model uses $h(x)=e^{3x}$. What is the value of the third derivative $h^{(3)}(x)$?

$9e^{3x}$

$27e^{3x}$

$27e^{x}$

$81e^{3x}$

$3e^{3x}$

Explanation

For h(x) = e³ˣ, finding the third derivative requires applying the chain rule three times. First, h'(x) = e³ˣ · 3 = 3e³ˣ. Second, h''(x) = 3e³ˣ · 3 = 9e³ˣ. Third, h'''(x) = 9e³ˣ · 3 = 27e³ˣ. Notice the pattern: each differentiation multiplies by 3 (the coefficient in the exponent), so the nth derivative is 3ⁿe³ˣ. A common mistake is forgetting to apply the chain rule at each step or losing track of the accumulating coefficients. For exponential functions with linear exponents like e^(ax), the nth derivative follows the pattern aⁿe^(ax), making higher-order derivatives predictable.

4

Let $s(x)=\cos(3x)$. What is $s''(x)$?

$9\sin(3x)$

$-9\cos(3x)$

$-3\sin(3x)$

$-9\sin(3x)$

$9\cos(3x)$

Explanation

To find s''(x) for s(x) = cos(3x), we apply the chain rule twice. First, s'(x) = -sin(3x)·3 = -3sin(3x). Then s''(x) = -3cos(3x)·3 = -9cos(3x). The pattern emerges: each differentiation introduces a factor of 3 (from the chain rule) and cycles through cos → -sin → -cos → sin. A common mistake is forgetting to multiply by the derivative of the inner function (3) at each step. For trig functions with linear arguments, remember that the nth derivative introduces a factor of the argument's coefficient raised to the nth power.

5

Let $u(x)=x^2\ln x$ for $x>0$. What is $u''(x)$?

$2\ln x+3$

$2x\ln x+3x$

$2\ln x+1$

$2x\ln x+x$

$2\ln x+2$

Explanation

For u(x) = x²ln x where x > 0, we need the product rule twice. First, u'(x) = 2x ln x + x²(1/x) = 2x ln x + x. For the second derivative, differentiate each term: d/dx(2x ln x) = 2ln x + 2x(1/x) = 2ln x + 2, and d/dx(x) = 1. Therefore, u''(x) = 2ln x + 2 + 1 = 2ln x + 3. A common error is forgetting that d/dx(ln x) = 1/x when applying the product rule to the first term. Always carefully track each application of differentiation rules when products involve logarithms.

6

For $f(x)=\tan(x)$, what is the second derivative $f''(x)$?

$f''(x)=2 sin(x) sec^3(x)$

$f''(x)=-2 sec^2(x) tan(x)$

$f''(x)= sec(x) tan(x)$

$f''(x)=2 sec^2(x) tan(x)$

$f''(x)= sec^2(x)$

Explanation

Tangent's derivatives involve secant and tangent terms. The first is f'(x) = $sec^2$(x). The second is f''(x) = 2 $sec^2$(x) tan(x), using chain rule. A common stopping error is only computing the first. Express in trig identities if simplifying. A transferable strategy for trig derivatives is to use known identities and chain rule repeatedly.

7

For $f(x)=3x^4-5x^2+7x$, what is $f''(x)$?

$36x^2-10$

$36x^2-10x$

$12x^3-10x+7$

$36x^2+10$

$12x^3-10x$

Explanation

To find the second derivative f''(x) of f(x) = 3x⁴ - 5x² + 7x, we need to differentiate twice. First, f'(x) = 12x³ - 10x + 7 using the power rule. Then, differentiating again gives f''(x) = 36x² - 10. A common error is stopping after the first derivative or forgetting to differentiate the constant term (which becomes 0). Notice how the degree decreases by 1 with each differentiation. For polynomial functions, systematically apply the power rule to each term, reducing the exponent by 1 and multiplying by the original exponent each time.

8

Let $q(x)=e^{2x}$. What is $q^{(3)}(x)$?

$4e^{2x}$

$12e^{2x}$

$6e^{2x}$

$8e^{2x}$

$2e^{2x}$

Explanation

For q(x) = e^(2x), we need the third derivative q'''(x). Using the chain rule repeatedly: q'(x) = 2e^(2x), q''(x) = 4e^(2x), and q'''(x) = 8e^(2x). Each differentiation multiplies by the derivative of the exponent (which is 2), giving us powers of 2: 2¹, 2², 2³. A common mistake is forgetting to apply the chain rule consistently or losing track of the coefficient. For exponential functions with linear exponents, the nth derivative of e^(kx) is $k^n$·e^(kx).

9

Let $f(x)=\ln(5x)$. What is the second derivative $f''(x)$ for $x>0$?

$f''(x)=-rac{1}{5x^2}$

$f''(x)=rac{1}{x^2}$

$f''(x)=-rac{5}{x^2}$

$f''(x)=-rac{1}{x^2}$

$f''(x)=rac{1}{x}$

Explanation

Logarithmic derivatives simplify, but higher orders need care. The first is f'(x) = 1/x. The second is f''(x) = $-1/x^2$, with negative sign. A common error is stopping at first or ignoring the constant in ln(5x). Domain x > 0. For logs, differentiate successively, noting inverse square patterns.

10

Let $f(x)=(1-x)^4$. What is the second derivative $f''(x)$?

$f''(x)=4(1-x)^3$

$f''(x)=-12(1-x)^2$

$f''(x)=12(1-x)^3$

$f''(x)=12(1-x)^2$

$f''(x)=24(1-x)$

Explanation

Binomial powers differentiate with chain rule and signs. The first is f'(x) = -4(1 - $x)^3$. The second is f''(x) = 12(1 - $x)^2$, flipping positive. A common stopping error is only first derivative. Note the sign changes from the inner derivative. A transferable strategy is to apply chain rule multiple times, tracking the inner function's derivative.

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