微积分I(标准路径) · 免费预览

§3.3 Using derivatives to identify extreme values (continued)

函数 $f$ 的临界数是什么?它们与确定该函数所能取得的最极端的值之间有什么联系?

1. Summary

Summary

2. Sign chart from a derivative graph

A graph of f′f' shows f′f' negative for x<−1x \lt -1, positive for −1<x<1-1 \lt x \lt 1, and positive for x>1x \gt 1, with f(0)=−12f(0) = -\frac{1}{2}. The function ff has

3. Inflection points from the same graph

The same graph of f′f' shows horizontal tangents at about x=−0.35x = -0.35 and x=1x = 1, with f′f' steepest between them. The inflection points of ff occur at

4. A plateau that is neither peak nor valley

Suppose g′(2)=0g'(2) = 0 and g′(x)>0g'(x) \gt 0 on both 1<x<21 \lt x \lt 2 and 2<x<32 \lt x \lt 3. At x=2x = 2 the function gg has

5. What is special about the flat point

With g′(2)=0g'(2) = 0, g′>0g' \gt 0 nearby, and g′′g'' existing on 1<x<31 \lt x \lt 3, the value x=2x = 2 is special because

6. Roots of a function from its derivative graph

A graph of h′h' shows h′<0h' \lt 0 for x<0x \lt 0 and h′>0h' \gt 0 for x>0x \gt 0, with h′h' tending to 33 as x→∞x \to \infty. If h(x)=0h(x) = 0 has two distinct real solutions, their signs must be

7. Long run appearance of the graph

With the same h′h' approaching 33 as x→∞x \to \infty, the graph of y=h(x)y = h(x) for large xx looks like

8. A rational derivative with a vertical asymptote

Let g′(x)=(x+4)(x−1)2x−2g'(x) = \frac{(x+4)(x-1)^2}{x-2} with gg having a vertical asymptote at x=2x = 2. The critical numbers of gg and their classification are

9. Long term behavior from a rational derivative

For the same gg, the value of lim⁡x→∞g′(x)\lim_{x \to \infty} g'(x) and its meaning are

10. Second derivative test with a formula

Let p′′(x)=(x+1)(x−2)e−xp''(x) = (x+1)(x-2)e^{-x}. The critical number x=5−12≈0.618x = \frac{\sqrt{5}-1}{2} \approx 0.618 lies between −1-1 and 22, so pp has

11. Inflection inventory

With the same p′′(x)=(x+1)(x−2)e−xp''(x) = (x+1)(x-2)e^{-x}, the inflection points of pp occur at

12. Tangent line above or below at an inflection

The point (2,12e2)(2, \frac{12}{e^2}) lies on y=p(x)y = p(x) with p′(2)=−5e2p'(2) = -\frac{5}{e^2}, and x=2x = 2 is an inflection point. The tangent line at x=2x = 2 lies

13. Evaluating the second derivative

For p′′(x)=(x+1)(x−2)e−xp''(x) = (x+1)(x-2)e^{-x}, compute p′′(0)p''(0).

14. Locating the golden ratio critical number

The critical number 5−12\frac{\sqrt{5}-1}{2} appears in the study of pp. Compute its decimal value, rounded to three places.

15. Inflection needs a sign change

If g′′(2)=0g''(2) = 0 and g′′g'' changes sign at x=2x = 2, then gg has an inflection point at x=2x = 2.

进入交互式练习

免费注册 · 即时批改 · 自动安排间隔复习。

免费开始这门课