5. The continuous function \( f \) is defined on the interval \( -3 \leq x \leq 6 \). The graph of \( f \) consists of two quarter circles and two line segments, as shown in the figure above. Which of the following statements must be true?

I. The average rate of change of \( f \) on the interval \( -3 \leq x \leq 6 \) is \( \frac{1}{9} \).

II. There is a point \( c \) on the interval \( -3 < x < 6 \), for which \( f'(c) \) is equal to the average rate of change of \( f \) on the interval \( -3 \leq x \leq 6 \).

III. If \( h \) is the function given by \( h(x) = f\left( \frac{1}{2} x \right) \), then \( h'(6) = -\frac{1}{2} \).






Answer is: option2

I and III only

Solution:

The average rate of change of a function \( f(x) \) over the interval \([a, b]\) is given by:

\[ \text{Average Rate of Change} = \frac{f(b) - f(a)}{b - a} \]

From the graph:

  • \( f(-3) = 0 \)
  • \( f(6) = -1 \)

So, the average rate of change over \([-3,6]\) is:

\[ \frac{f(6) - f(-3)}{6 - (-3)} = \frac{-1 - 0}{6 + 3} = \frac{-1}{9} \]

This matches Statement I, so it is true.

The quarter-circle sections have positive slopes.

The line segment from (2,3) to (6,-1) has slope:

\[ \frac{-1 - 3}{6 - 2} = \frac{-4}{4} = -1 \]

which is much steeper than \(-\frac{1}{9}\).

Since nowhere on the differentiable sections does the slope equal \(-\frac{1}{9}\), there is no point \( c \) where \( f'(c) = -\frac{1}{9} \).

Statement II is false because no such \( c \) exists.

Given:

\[ h(x) = f\left(\frac{1}{2} x\right) \]

Using the chain rule:

\[ h'(x) = f'\left(\frac{1}{2}x\right) \cdot \frac{d}{dx}\left(\frac{1}{2}x\right) = f'\left(\frac{1}{2}x\right) \cdot \frac{1}{2} \]

Evaluating at \( x = 6 \):

\[ h'(6) = f'\left(\frac{1}{2} \times 6\right) \cdot \frac{1}{2} = f'(3) \cdot \frac{1}{2} \]

From the graph, at \( x = 3 \), the function is decreasing at a slope of -1, so \( f'(3) = -1 \). Therefore:

\[ h'(6) = (-1) \times \frac{1}{2} = -\frac{1}{2} \]

This matches Statement III, so it is true.

Thus, the correct answer is (B) I and III only.

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