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Question

Which of the following is correct about first and second derivatives at points P, Q and R for $f(x) = \sin(x)$ shown below?

The correct answer is

$ \frac{d^2f}{dx^2}|_P < 0; \frac{d^2f}{dx^2}|_Q = 0; \frac{d^2f}{dx^2}|_R > 0$

To solve this problem, we need to analyze the behavior of the first and second derivatives of the function \(f(x) = \sin(x)\) at the points P, Q, and R in the given plot.

Let's break down the problem step by step:

  1. Consider the first and second derivatives of \(f(x) = \sin(x)\):
    • The first derivative is \(\frac{df}{dx} = \cos(x)\).
    • The second derivative is \(\frac{d^2f}{dx^2} = -\sin(x)\).
  2. Evaluate the derivatives at point P (maximum point):
    • At a maximum point, the first derivative \(\frac{df}{dx} = 0\) (since the slope is horizontal).
    • The second derivative is negative, \(\frac{d^2f}{dx^2} < 0\), indicating a local maximum. This is consistent with option (C).
  3. Evaluate the derivatives at point Q (inflection point):
    • At point Q, the second derivative \(\frac{d^2f}{dx^2} = -\sin(x) = 0\), indicating an inflection point where the concavity changes. This matches option (C).
  4. Evaluate the derivatives at point R (minimum point):
    • At a minimum point, the first derivative \(\frac{df}{dx} = 0\) (slope is again horizontal).
    • The second derivative is positive, \(\frac{d^2f}{dx^2} > 0\), indicating a local minimum. This aligns with option (C).

Based on the analysis above, we conclude that the correct answer is option (C), which states:

\(\frac{d^2f}{dx^2}|_P < 0; \frac{d^2f}{dx^2}|_Q = 0; \frac{d^2f}{dx^2}|_R > 0\)

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Important Questions from Calculus

  1. f(x) = 2x2 – 1, then f(0) = _______.
  2. Find the value of integral I = \(\smallint \frac{1}{{x + \sqrt x }}\)dx. (where c = constant)

  3. Differentiate (a cos 3t) w.r.t. to (a sin 3t)

  4. Find the slope of normal to the curve y = x2 + 7x at (1, 8).

  5. Find the equation of normal to the curve y = 4x - 3x2 at (2, -4).

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