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§1.3 The derivative of a function at a point (continued)

函数在给定区间上的平均变化率是如何定义的?这个量度量的是什么?

1. Summary

Summary

2. Matching slopes to lines on a graph

For a smooth function ff, measurements give the secant slope on [−3,−1][-3,-1] as about 1.151.15, the secant slope on [0,2][0,2] as about −0.4-0.4, the tangent slope at x=−3x = -3 as about 33, and the tangent slope at x=0x = 0 as about −0.5-0.5. Which pairing of quantity and slope is correct?

3. Building a target average rate

A sketch must show a function ff with f(−3)=3f(-3) = 3 whose average rate of change on [−3,0][-3, 0] equals −2-2. What value of f(0)f(0) produces that average rate?

4. Total population change

With P(t)=1.15(1.014)tP(t) = 1.15(1.014)^t billion people, compute the total change in population between the start of 1993 and the start of 2000. Give your answer in billions of people, rounded to four decimal places.

5. Total change versus average rate

China's population is modeled by P(t)=1.15(1.014)tP(t) = 1.15(1.014)^t billion people with tt years since the start of 1993. What is the average rate of change of the population over [0,7][0, 7]?

6. Comparing an instantaneous with an average growth rate

For the model P(t)=1.15(1.014)tP(t) = 1.15(1.014)^t, computations give AV[0,7]≈0.0168AV_{[0,7]} \approx 0.0168 and P′(7)≈0.0180P'(7) \approx 0.0180 billion people per year. How do these compare, and why?

7. Definition of the derivative at zero

For P(t)=1.15(1.014)tP(t) = 1.15(1.014)^t, the instantaneous growth rate at the start of 1993 is P′(0)=lim⁡h→0P(h)−P(0)hP'(0) = \displaystyle\lim_{h \to 0} \frac{P(h) - P(0)}{h}.

8. Derivative of a quadratic at a point

Use the limit definition to compute f′(2)f'(2) for f(x)=x2−3xf(x) = x^2 - 3x.

9. Derivative of a reciprocal at a point

Use the limit definition to compute f′(1)f'(1) for f(x)=1xf(x) = \frac{1}{x}.

10. A corner blocks the derivative

Let f(x)=2−∣x−1∣f(x) = 2 - |x - 1|. Difference quotients at a=1a = 1 give 11 for h<0h \lt 0 and −1-1 for h>0h \gt 0. What does this mean for f′(1)f'(1)?

11. A horizontal tangent for the sine

For f(x)=sin⁡(x)f(x) = \sin(x), the point (π2,1)(\frac{\pi}{2}, 1) is the top of a hump in the graph, and the data indicate f′(π2)=0f'\left(\frac{\pi}{2}\right) = 0.

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