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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. The Derivative of a Function at a Point

The Derivative of a Function at a Point

2. Derivative from the definition for a quadratic

Use the limit definition to compute f′(2)f'(2) for f(x)=x−x2f(x) = x - x^2.

3. Slope of a linear function anywhere

Let f(x)=3−2xf(x) = 3 - 2x, a linear function. Using any valid method, what are f′(2)f'(2), f′(π)f'(\pi), and f′(−2)f'(-\sqrt{2})?

4. Averages and instant rates for a linear function

For f(x)=3−2xf(x) = 3 - 2x, the average rates of change on [1,4][1,4], on [3,7][3,7], on [5,5+h][5,5+h], and the instantaneous rate f′(1)f'(1) all equal −2-2.

5. Key features of a tossed ball's height graph

A ball's height is s(t)=−16t2+16t+32s(t) = -16t^2 + 16t + 32 feet. Which list correctly gives the intercepts and vertex of the graph of ss?

6. Average velocity of the tossed ball

For s(t)=−16t2+16t+32s(t) = -16t^2 + 16t + 32 feet with tt in seconds, compute the average velocity on the interval [1,2][1, 2], in feet per second.

7. Instantaneous velocity of a tossed ball

A ball's height is s(t)=−16t2+16t+32s(t) = -16t^2 + 16t + 32 feet at time tt seconds. Using the limit definition, what is s′(1)s'(1)?

8. Secant and tangent lines for the ball

For the ball with s(t)=−16t2+16t+32s(t) = -16t^2 + 16t + 32 and the population P(t)=25000et/5P(t) = 25000e^{t/5}, two lines are drawn at each of t=1t = 1 and t=2t = 2 respectively: one through the curve points at the ends of an interval starting there, one just touching the curve at that instant. What do the two kinds of lines represent?

9. Where the ball's derivative is positive

For s(t)=−16t2+16t+32s(t) = -16t^2 + 16t + 32 on the ball's flight from t=0t = 0 to t=2t = 2, where is s′(a)s'(a) positive, zero, and negative?

10. Average growth rate of a city

A city's population is P(t)=25000et/5P(t) = 25000e^{t/5} people with tt in decades from today. Compute the average rate of change of PP between t=2t = 2 and t=4t = 4 (years 2030 to 2050). Round to the nearest person per decade.

11. Why an exponential limit resists algebra

For P(t)=25000et/5P(t) = 25000e^{t/5}, the limit definition gives P′(2)=lim⁡h→025000e2/5(eh/5−1h)P'(2) = \lim_{h \to 0} 25000e^{2/5}\left(\frac{e^{h/5}-1}{h}\right). Why is this limit difficult to evaluate exactly?

12. Estimating an instantaneous rate numerically

A city's population is P(t)=25000et/5P(t) = 25000e^{t/5} people with tt in decades. Numerical work gives average growth rates over [2−h,2][2-h, 2] near 74607460 and over [2,2+h][2, 2+h] near 74577457 people per decade. The best estimate of P′(2)P'(2) is about

13. Growth and steepening of an exponential model

A city's population follows P(t)=25000et/5P(t) = 25000e^{t/5} with tt in decades. As tt increases from 00 to 55, what do the graph of PP and its tangent slopes P′(a)P'(a) do?

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