Second Derivative Test
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AP Calculus BC › Second Derivative Test
The function $s$ has a critical point at $x=-2$ and $s''(-2)=9$; classify $x=-2$.
A relative minimum at $x=-2$
Cannot be determined because $s''(-2)>0$
A point of inflection at $x=-2$
Neither a maximum nor minimum at $x=-2$ because it is a critical point
A relative maximum at $x=-2$
Explanation
This problem requires the Second Derivative Test to classify critical points of a function. The test identifies a relative minimum when s'(c) = 0 and s''(c) > 0, showing concave up. Here, x = -2 is a critical point, and s''(-2) = 9 > 0 indicates upward concavity. This positive concavity forms a local trough where the graph bends up. A tempting distractor is choice B, a relative maximum, but positive second derivatives denote minima, not maxima. Ensure the point is indeed critical and the second derivative non-zero to qualify for the test's conclusive application.
If $M'(!-6)=0$ and $M''(!-6)=-1$, what does the Second Derivative Test conclude at $x=-6$?
Neither; the test is inconclusive because $M''(-6)<0$
Local maximum at $x=-6$
Local minimum at $x=-6$
Neither; $M''(-6)<0$ implies concave up
Cannot be determined without $M(-6)$
Explanation
The Second Derivative Test is a method to classify critical points of a function by examining the sign of the second derivative at those points. At x=-6, M'(-6)=0 marks a critical point, and M''(-6)=-1, negative, indicates concave down. This suggests a local maximum, as the graph peaks there. The negative value ensures decreasing function away from the point. A tempting distractor is choice B, which claims M''(-6)<0 implies concave up, but it means concave down. To apply the Second Derivative Test effectively, always ensure the first derivative is zero and check if the second derivative is non-zero; if it is zero, switch to the First Derivative Test for classification.
A differentiable function $F$ has $F'(\pi)=0$ and $F''(\pi)=2$; classify the critical point at $x=\pi$.
Neither a maximum nor minimum at $x=\pi$ because $F''(\pi)>0$
Cannot be determined because $\pi$ is irrational
A relative maximum at $x=\pi$
A relative minimum at $x=\pi$
A point of inflection at $x=\pi$
Explanation
This problem requires the Second Derivative Test to classify critical points of a function. The test states that F'(c) = 0 and F''(c) > 0 imply a relative minimum due to concave up. For F, F'(π) = 0 marks the critical point, and F''(π) = 2 > 0 shows upward concavity. This positive value means the graph forms a local minimum at x = π. A tempting distractor is choice A, a relative maximum, but this would require a negative second derivative instead. A transferable strategy is to first locate critical points where the first derivative is zero, then check the second derivative's sign for classification.
A function has $G'(!-\pi)=0$ and $G''(!-\pi)=5$; classify the critical point at $x=-\pi$.
Neither; $G''(-\pi)>0$ implies a local maximum
Cannot be determined without $G(-\pi)$
Local minimum at $x=-\pi$
Neither; the test is inconclusive because $G''(-\pi)>0$
Local maximum at $x=-\pi$
Explanation
The Second Derivative Test is a method to classify critical points of a function by examining the sign of the second derivative at those points. At x=-π, G'(-π)=0 indicates a critical point, and G''(-π)=5, positive, shows concave up. This upward curve suggests a local minimum. The function forms a valley there, increasing away. A tempting distractor is choice B, which incorrectly states G''(-π)>0 implies a local maximum, but positive means minimum. To apply the Second Derivative Test effectively, always ensure the first derivative is zero and check if the second derivative is non-zero; if it is zero, switch to the First Derivative Test for classification.
Suppose $k'(\tfrac{1}{2})=0$ and $k''(\tfrac{1}{2})=3$; what is the classification at $x=\tfrac{1}{2}$?
Local maximum at $x=\tfrac{1}{2}$
Neither; the test is inconclusive because $k''(\tfrac{1}{2})\neq 0$
Local minimum at $x=\tfrac{1}{2}$
Cannot be determined without checking $k'(x)$ on both sides
Neither; it must be an inflection point
Explanation
The Second Derivative Test is a method to classify critical points of a function by examining the sign of the second derivative at those points. At x=1/2, k'(1/2)=0 marks a critical point, and k''(1/2)=3, positive, indicates concave up. Concave up implies a minimum point, as the graph curves upward like a bowl. Thus, there is a local minimum at x=1/2, with function values rising away from it. A tempting distractor is choice D, which assumes it must be an inflection point, but positive f'' confirms a minimum, not a concavity change. To apply the Second Derivative Test effectively, always ensure the first derivative is zero and check if the second derivative is non-zero; if it is zero, switch to the First Derivative Test for classification.
Suppose $b'(3)=0$ and $b''(3)=-\tfrac{1}{5}$; classify the critical point at $x=3$.
Neither; the test is inconclusive because $b'(3)=0$
Local minimum at $x=3$
Local maximum at $x=3$
Neither; $b''(3)<0$ implies concave up
Cannot be determined without checking $b''(x)$ near $3$
Explanation
The Second Derivative Test classifies critical points by checking the second derivative's sign at locations where the first derivative is zero. If negative, like b''(3) = -1/5 < 0, the function is concave down, indicating a peak. This means the point is higher than its neighbors, marking a local maximum. Therefore, x = 3 is a local maximum. Some might think negative implies concave up, but that's incorrect; negative denotes concave down. Ensure the critical point is isolated and the function smooth to apply the test across various functions.
A differentiable function has $c'(!-1)=0$ and $c''(!-1)=0$; what can be concluded at $x=-1$?
The test is inconclusive at $x=-1$
Local maximum at $x=-1$
Neither; $c''(-1)=0$ implies concave down
Neither; it must be an inflection point
Local minimum at $x=-1$
Explanation
The Second Derivative Test is applied to critical points to determine their nature through the second derivative. When the second derivative is zero, as with c''(-1) = 0, concavity doesn't clearly indicate a max or min. It could be either or neither, like an inflection point or flat spot. Thus, the test is inconclusive here. A distractor suggesting it's necessarily an inflection point fails because zero second derivative alone doesn't confirm a concavity change; further checks are needed. Always confirm if higher derivatives or other tests like the first derivative test can resolve inconclusive cases.
Given $r'(!-\tfrac{5}{4})=0$ and $r''(!-\tfrac{5}{4})=\tfrac{16}{3}$, what is the classification at $x=-\tfrac{5}{4}$?
Neither; it must be an inflection point
Local maximum at $x=-\tfrac{5}{4}$
Cannot be determined without checking $r'(x)$
Neither; the test is inconclusive because $r''(-\tfrac{5}{4})\neq 0$
Local minimum at $x=-\tfrac{5}{4}$
Explanation
Employing the Second Derivative Test, positive derivatives indicate minima. r''(-5/4) = 16/3 > 0 means concave up, local minimum. Graph bottoms locally. So, x = -5/4 is a local minimum. Needing f value is unnecessary; test uses derivatives only. Confirm differentiability for application strategy.
A function satisfies $g'(!-9)=0$ and $g''(!-9)=-\tfrac{11}{3}$; what is the classification at $x=-9$?
Local minimum at $x=-9$
Cannot be determined without checking $g'(x)$
Local maximum at $x=-9$
Neither; $g''(-9)<0$ implies concave up
Neither; the test is inconclusive because $g''(-9)\neq 0$
Explanation
The Second Derivative Test assesses concavity for critical point classification. A negative second derivative, g''(-9) = -11/3 < 0, shows concave down, indicating a local maximum. Values decrease from this peak. Therefore, x = -9 is a local maximum. The idea that negative implies concave up is false; it's the opposite. Always check if the first derivative changes sign or use alternatives if inconclusive.
For differentiable $r$, $r'(0)=0$ and $r''(0)=-9$. Which statement correctly classifies $x=0$?
Point of inflection at $x=0$ because $r'(0)=0$.
The Second Derivative Test is inconclusive at $x=0$.
Local maximum at $x=0$ because $r''(0)<0$.
Cannot be determined without checking $r'(x)$ sign changes.
Local minimum at $x=0$ because $r''(0)<0$.
Explanation
This problem applies the Second Derivative Test with a negative second derivative. We have r'(0) = 0 (critical point) and r''(0) = -9 < 0. According to the Second Derivative Test, when f'(c) = 0 and f''(c) < 0, the function has a local maximum at x = c. The negative second derivative indicates concave down behavior, creating a hill shape at x = 0. Choice A reverses the relationship, incorrectly pairing negative concavity with a minimum. For test success, remember the mnemonic: "negative second derivative = frown shape = maximum" and "positive second derivative = smile shape = minimum."