Determining Limits Using the Squeeze Theorem

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AP Calculus BC › Determining Limits Using the Squeeze Theorem

Questions 1 - 10
1

If $\dfrac{\sin x}{x}\le p(x)\le \dfrac{\sin x}{x}+x^2$ near $0$, what is $\lim_{x\to 0} p(x)$?

$-1$

$0$

Does not exist

$1$

$\lim_{x\to 0}\left(\dfrac{\sin x}{x}+x^2\right)$

Explanation

This problem utilizes the squeeze theorem to find the limit of p(x) as x approaches 0. The function is bounded below by (sin x)/x and above by (sin x)/x + x² near 0. As x approaches 0, both bounds approach 1. Therefore, by the squeeze theorem, p(x) must also approach 1. A tempting distractor is A, 0, perhaps if one confuses it with lim x² alone. A transferable squeeze recognition strategy is to identify bounds that both converge to the same value, forcing the sandwiched term to do the same.

2

Given $-\dfrac{|x|^3}{7} \le g(x) \le \dfrac{|x|^3}{7}$ near $0$, find $\lim_{x\to 0} g(x)$.

$\infty$

Does not exist

$0$

$\dfrac{1}{7}$

$-\dfrac{1}{7}$

Explanation

This problem utilizes the squeeze theorem to find the limit of g(x) as x approaches 0. The function is bounded below by $-\frac{|x|^3}{7}$ and above by $\frac{|x|^3}{7}$ near 0. As x approaches 0, both bounds approach 0. Therefore, by the squeeze theorem, g(x) must also approach 0. A tempting distractor is A, $\frac{1}{7}$, perhaps if one ignores the $|x|^3$ term. A transferable squeeze recognition strategy is to identify bounds that both converge to the same value, forcing the sandwiched term to do the same.

3

If $\dfrac{\arctan x}{x}\le S(x)\le 1$ near $0$, what is $\lim_{x\to 0} S(x)$?

$\dfrac{\pi}{2}$

$0$

Does not exist

$1$

$\lim_{x\to 0}\dfrac{\arctan x}{x}$

Explanation

This problem utilizes the squeeze theorem to find the limit of S(x) as x approaches 0. The function is bounded below by $\dfrac{\arctan x}{x}$ and above by 1 near 0. As x approaches 0, $\dfrac{\arctan x}{x}$ approaches 1 and 1 approaches 1. Therefore, by the squeeze theorem, S(x) must also approach 1. A tempting distractor is A, 0, perhaps if one confuses the limit with that of $\arctan x$ itself. A transferable squeeze recognition strategy is to identify bounds that both converge to the same value, forcing the sandwiched term to do the same.

4

Suppose $\dfrac{\sin^2 x}{x^2}\le Y(x)\le 1$ for $x$ near $0$, find $\lim_{x\to 0} Y(x)$.

$1$

$0$

Does not exist

$\lim_{x\to 0}\dfrac{\sin^2 x}{x^2}$

$-1$

Explanation

This problem utilizes the squeeze theorem to find the limit of Y(x) as x approaches 0. The function is bounded below by sin²x / x² and above by 1 near 0. As x approaches 0, sin²x / x² approaches 1 and 1 approaches 1. Therefore, by the squeeze theorem, Y(x) must also approach 1. A tempting distractor is A, 0, perhaps if one confuses it with lim sin x / x without squaring. A transferable squeeze recognition strategy is to identify bounds that both converge to the same value, forcing the sandwiched term to do the same.

5

Given $2x^2\le V(x)\le 5x^2$ near $0$, what is $\lim_{x\to 0} V(x)$?

Does not exist

$5$

$0$

$2$

$\lim_{x\to 0}(2x^2)$

Explanation

This problem utilizes the squeeze theorem to find the limit of V(x) as x approaches 0. The function is bounded below by 2x² and above by 5x² near 0. As x approaches 0, both 2x² and 5x² approach 0. Therefore, by the squeeze theorem, V(x) must also approach 0. A tempting distractor is B, 5, perhaps if one mistakenly takes the coefficient of the upper bound as the limit. A transferable squeeze recognition strategy is to identify bounds that both converge to the same value, forcing the sandwiched term to do the same.

6

Suppose $\dfrac{1}{x}-\dfrac{3}{x^2}\le j(x)\le \dfrac{1}{x}+\dfrac{3}{x^2}$ for large $x$; find $\lim_{x\to\infty} x,j(x)$.

$0$

$\infty$

$3$

$1$

$-\infty$

Explanation

This problem utilizes the squeeze theorem to find the limit of x j(x) as x approaches infinity. The function j(x) is bounded below by 1/x - 3/x² and above by 1/x + 3/x² for large x, so x j(x) is bounded by 1 - 3/x and 1 + 3/x. As x approaches infinity, both 1 - 3/x and 1 + 3/x approach 1. Therefore, by the squeeze theorem, x j(x) must also approach 1. A tempting distractor is C, 3, perhaps if one focuses on the coefficient 3 without multiplying by x. A transferable squeeze recognition strategy is to identify bounds that both converge to the same value, forcing the sandwiched term to do the same.

7

If $\dfrac{1}{x+1}-\dfrac{1}{x^2}\le U(x)\le \dfrac{1}{x+1}+\dfrac{1}{x^2}$ for large $x$, find $\lim_{x\to\infty} U(x)$.

$1$

$\infty$

$0$

$-1$

$\lim_{x\to\infty}\dfrac{1}{x+1}$

Explanation

This problem utilizes the squeeze theorem to find the limit of U(x) as $x \to \infty$. The function is bounded below by $\frac{1}{x+1} - \frac{1}{x^2}$ and above by $\frac{1}{x+1} + \frac{1}{x^2}$ for large $x$. As $x \to \infty$, both bounds approach $0$. Therefore, by the squeeze theorem, U(x) must also approach $0$. A tempting distractor is A, $1$, perhaps if one ignores the added terms and focuses only on $\frac{1}{x+1}$. A transferable squeeze recognition strategy is to identify bounds that both converge to the same value, forcing the sandwiched term to do the same.

8

Given $-\dfrac{(x+2)^3}{10}\le H(x)\le \dfrac{(x+2)^3}{10}$ near $x=-2$, find $\lim_{x\to -2} H(x)$.

$0$

$-2$

Does not exist

$-\dfrac{1}{10}$

$\dfrac{1}{10}$

Explanation

This problem requires the squeeze theorem to determine the limit of H(x) as x approaches -2. The function H(x) is bounded below by $-(x+2)^3$/10 and above by $(x+2)^3$/10, both approaching 0 as x approaches -2. Since $lim_{x→-2}$ $-(x+2)^3$/10 = 0 and $lim_{x→-2}$ $(x+2)^3$/10 = 0, the squeeze theorem implies $lim_{x→-2}$ H(x) = 0. The cubic terms vanish at the point. A tempting distractor is choice E, does not exist, perhaps due to the odd power's sign change. A transferable squeeze recognition strategy is to check if higher-odd-power bounds still converge to zero.

9

If $-\dfrac{|x-1|}{2}\le z(x)\le \dfrac{|x-1|}{2}$ near $x=1$, find $\lim_{x\to 1} z(x)$.

Does not exist

$0$

$-\dfrac{1}{2}$

$\dfrac{1}{2}$

$1$

Explanation

This problem requires the squeeze theorem to determine the limit of z(x) as x approaches 1. The function z(x) is bounded below by -|x-1|/2 and above by |x-1|/2, both approaching 0 as x approaches 1. Since $lim_{x→1}$ -|x-1|/2 = 0 and $lim_{x→1}$ |x-1|/2 = 0, the squeeze theorem guarantees $lim_{x→1}$ z(x) = 0. The absolute value creates linear convergence to zero. A tempting distractor is choice E, does not exist, maybe due to the absolute value's kink. A transferable squeeze recognition strategy is to employ absolute value bounds for limits at non-zero points.

10

Suppose $-\sqrt{|x|}\le T(x)\le \sqrt{|x|}$ near $0$; find $\lim_{x\to 0} T(x)$.

$\lim_{x\to 0}\sqrt{|x|}$

$1$

$-1$

Does not exist

$0$

Explanation

This problem utilizes the squeeze theorem to find the limit of T(x) as x approaches 0. The function is bounded below by -√|x| and above by √|x| near 0. As x approaches 0, both -√|x| and √|x| approach 0. Therefore, by the squeeze theorem, T(x) must also approach 0. A tempting distractor is E, 'Does not exist,' perhaps if one thinks the absolute value causes oscillation, but the bounds converge. A transferable squeeze recognition strategy is to identify bounds that both converge to the same value, forcing the sandwiched term to do the same.

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