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AP Calculus AB Flashcards: Lhospitals Rule

Study Lhospitals Rule in AP Calculus AB with focused flashcards that help you recognize the idea, recall the key rule, and apply it in practice-style prompts.

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What this deck covers

This deck focuses on Lhospitals Rule, giving you a quick way to review the definitions, rules, and examples that matter most for AP Calculus AB.

How to use these flashcards

Work through these flashcards in short sessions. Try to answer each prompt before flipping the card, then revisit any cards you miss until the explanation feels automatic.

AP Calculus AB Flashcards: Lhospitals Rule

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QUESTION

What must be true of f(x)f(x)f(x) and g(x)g(x)g(x) in L'Hospital's Rule?

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ANSWER

f(x)f(x)f(x) and g(x)g(x)g(x) must be differentiable near ccc. Functions must be differentiable for L'Hospital's Rule to work.

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Flashcard 1: What must be true of f(x)f(x)f(x) and g(x)g(x)g(x) in L'Hospital's Rule?

Answer: f(x)f(x)f(x) and g(x)g(x)g(x) must be differentiable near ccc. Functions must be differentiable for L'Hospital's Rule to work.

Flashcard 2: Find the limit: lim⁡x→0tan⁡xx\lim_{x \to 0} \frac{\tan x}{x}limx→0​xtanx​ using L'Hospital's Rule.

Answer:

  1. Derivative of tan⁡x\tan xtanx is sec⁡2x\sec^2 xsec2x; sec⁡201=1\frac{\sec^2 0}{1} = 11sec20​=1.

Flashcard 3: Define indeterminate form.

Answer: A form like 00\frac{0}{0}00​ or ∞∞\frac{\infty}{\infty}∞∞​ where limits are not immediately obvious. Forms where direct evaluation is unclear or undefined.

Flashcard 4: Identify the indeterminate form: lim⁡x→01−cos⁡xx2\lim_{x \to 0} \frac{1 - \cos x}{x^2}limx→0​x21−cosx​.

Answer: 00\frac{0}{0}00​. Both 1−cos⁡0=01 - \cos 0 = 01−cos0=0 and 02=00^2 = 002=0 give 00\frac{0}{0}00​.

Flashcard 5: What must the original limit be for L'Hospital's Rule to apply?

Answer: An indeterminate form. L'Hospital's Rule requires indeterminate forms to be valid.

Flashcard 6: Find the derivative of tan⁡x\tan xtanx for L'Hospital's Rule.

Answer: sec⁡2x\sec^2 xsec2x. Derivative of tangent function.

Flashcard 7: List a requirement for L'Hospital's Rule to be valid.

Answer: Both f(x)f(x)f(x) and g(x)g(x)g(x) must approach 0 or ∞\infty∞ as x→cx \to cx→c. Essential condition for applying the rule correctly.

Flashcard 8: Identify the indeterminate form: lim⁡x→∞x2x2+x\lim_{x \to \infty} \frac{x^2}{x^2 + x}limx→∞​x2+xx2​.

Answer: ∞∞\frac{\infty}{\infty}∞∞​. Both numerator and denominator approach infinity.

Flashcard 9: Find the derivative of exe^xex needed for L'Hospital's Rule.

Answer: exe^xex. Basic exponential derivative.

Flashcard 10: Find the limit: lim⁡x→0x2sin⁡x\lim_{x \to 0} \frac{x^2}{\sin x}limx→0​sinxx2​ using L'Hospital's Rule.

Answer:

  1. Apply L'Hospital's Rule: lim⁡x→02xcos⁡x=0\lim_{x \to 0} \frac{2x}{\cos x} = 0limx→0​cosx2x​=0.

Flashcard 11: Find the limit using L'Hospital's Rule: lim⁡x→0ex−1x\lim_{x \to 0} \frac{e^x - 1}{x}limx→0​xex−1​.

Answer:

  1. Derivative of ex−1e^x - 1ex−1 is exe^xex; derivative of xxx is 111; e01=1\frac{e^0}{1} = 11e0​=1.

Flashcard 12: What is the derivative of sin⁡x\sin xsinx needed for L'Hospital's Rule?

Answer: cos⁡x\cos xcosx. Basic trigonometric derivative.

Flashcard 13: Find the limit: lim⁡x→∞x2ex\lim_{x \to \infty} \frac{x^2}{e^x}limx→∞​exx2​ using L'Hospital's Rule.

Answer:

  1. Apply L'Hospital's Rule repeatedly; exponential grows faster than polynomial.

Flashcard 14: State L'Hospital's Rule for ∞∞\frac{\infty}{\infty}∞∞​ form.

Answer: lim⁡x→cf(x)g(x)=lim⁡x→cf′(x)g′(x)\lim_{x \to c} \frac{f(x)}{g(x)} = \lim_{x \to c} \frac{f'(x)}{g'(x)}limx→c​g(x)f(x)​=limx→c​g′(x)f′(x)​ if ∞∞\frac{\infty}{\infty}∞∞​ form. Same rule applies for ∞∞\frac{\infty}{\infty}∞∞​ form.

Flashcard 15: What is L'Hospital's Rule used for?

Answer: Determining limits of indeterminate forms like 00\frac{0}{0}00​ or ∞∞\frac{\infty}{\infty}∞∞​. Applies when direct substitution gives undefined ratios.

Flashcard 16: State L'Hospital's Rule for 00\frac{0}{0}00​ form.

Answer: lim⁡x→cf(x)g(x)=lim⁡x→cf′(x)g′(x)\lim_{x \to c} \frac{f(x)}{g(x)} = \lim_{x \to c} \frac{f'(x)}{g'(x)}limx→c​g(x)f(x)​=limx→c​g′(x)f′(x)​ if 00\frac{0}{0}00​ form. Take derivatives of numerator and denominator separately.

Flashcard 17: Identify the indeterminate form: lim⁡x→0sin⁡xx\lim_{x \to 0} \frac{\sin x}{x}limx→0​xsinx​.

Answer: 00\frac{0}{0}00​. Both sin⁡0=0\sin 0 = 0sin0=0 and 000 in denominator give 00\frac{0}{0}00​.

Flashcard 18: Find the limit: lim⁡x→0ln⁡(1+x)x\lim_{x \to 0} \frac{\ln(1+x)}{x}limx→0​xln(1+x)​ using L'Hospital's Rule.

Answer:

  1. Derivative of ln⁡(1+x)\ln(1+x)ln(1+x) is 11+x\frac{1}{1+x}1+x1​; 11+01=1\frac{\frac{1}{1+0}}{1} = 111+01​​=1.

Flashcard 19: Identify the indeterminate form: lim⁡x→∞xex\lim_{x \to \infty} \frac{x}{e^x}limx→∞​exx​.

Answer: ∞∞\frac{\infty}{\infty}∞∞​. Both x→∞x \to \inftyx→∞ and ex→∞e^x \to \inftyex→∞ give ∞∞\frac{\infty}{\infty}∞∞​.

Flashcard 20: Find the derivative of ln⁡x\ln xlnx for L'Hospital's Rule.

Answer: 1x\frac{1}{x}x1​. Basic logarithmic derivative.

Flashcard 21: Find the limit: lim⁡x→1x3−1x−1\lim_{x \to 1} \frac{x^3 - 1}{x - 1}limx→1​x−1x3−1​ using L'Hospital's Rule.

Answer:

  1. Derivative of x3−1x^3 - 1x3−1 is 3x23x^23x2; derivative of x−1x - 1x−1 is 111; 3(1)21=3\frac{3(1)^2}{1} = 313(1)2​=3.

Flashcard 22: Find the limit: lim⁡x→∞ln⁡(x2)x\lim_{x \to \infty} \frac{\ln(x^2)}{x}limx→∞​xln(x2)​ using L'Hospital's Rule.

Answer:

  1. Use chain rule: derivative of ln⁡(x2)\ln(x^2)ln(x2) is 2x\frac{2}{x}x2​; limit is 000.

Flashcard 23: Find the derivative of sec⁡x\sec xsecx for L'Hospital's Rule.

Answer: sec⁡xtan⁡x\sec x \tan xsecxtanx. Derivative of secant function.

Flashcard 24: Find the limit: lim⁡x→01−cos⁡xx\lim_{x \to 0} \frac{1 - \cos x}{x}limx→0​x1−cosx​ using L'Hospital's Rule.

Answer:

  1. Derivative of 1−cos⁡x1 - \cos x1−cosx is sin⁡x\sin xsinx; sin⁡01=0\frac{\sin 0}{1} = 01sin0​=0.

Flashcard 25: Does L'Hospital's Rule apply to lim⁡x→01x\lim_{x \to 0} \frac{1}{x}limx→0​x1​?

Answer: No, it's not an indeterminate form. The limit approaches ±∞\pm\infty±∞, not an indeterminate form.

Flashcard 26: Find the derivative of cos⁡x\cos xcosx for L'Hospital's Rule.

Answer: −sin⁡x-\sin x−sinx. Basic trigonometric derivative.

Flashcard 27: Find the limit: lim⁡x→∞2x+3x+1\lim_{x \to \infty} \frac{2x + 3}{x + 1}limx→∞​x+12x+3​ using L'Hospital's Rule.

Answer:

  1. Apply L'Hospital's Rule: lim⁡x→∞21=2\lim_{x \to \infty} \frac{2}{1} = 2limx→∞​12​=2.

Flashcard 28: Identify the indeterminate form: lim⁡x→1x2−1x−1\lim_{x \to 1} \frac{x^2 - 1}{x - 1}limx→1​x−1x2−1​.

Answer: 00\frac{0}{0}00​. Factoring gives (x+1)(x−1)(x+1)(x-1)(x+1)(x−1) in numerator; creates 00\frac{0}{0}00​.

Flashcard 29: Find the derivative of ln⁡(1+x)\ln(1+x)ln(1+x) for L'Hospital's Rule.

Answer: 11+x\frac{1}{1+x}1+x1​. Chain rule derivative of logarithmic function.

Flashcard 30: Find the limit: lim⁡x→∞xx2+1\lim_{x \to \infty} \frac{x}{x^2 + 1}limx→∞​x2+1x​ using L'Hospital's Rule.

Answer:

  1. Apply L'Hospital's Rule: lim⁡x→∞12x=0\lim_{x \to \infty} \frac{1}{2x} = 0limx→∞​2x1​=0.