微积分I(标准路径) · free preview

§2.2 The sine and cosine functions (continued)

对于 $\frac{d}{dx}[a^x] = a^x \ln(a)$,如何给出图象上的直观解释?

1. Summary

Summary

2. Tangent line to a trig mix

For f(x)=3cos⁡(x)−2sin⁡(x)+6f(x) = 3\cos(x) - 2\sin(x) + 6, the tangent line approximation at a=πa = \pi is

3. Behavior at a quarter turn

For the same f(x)=3cos⁡(x)−2sin⁡(x)+6f(x) = 3\cos(x) - 2\sin(x) + 6, at x=π2x = \frac{\pi}{2} the function is

4. Interpreting a second derivative

An investment has value V(t)=24⋅1.07t+6sin⁡(t)V(t) = 24 \cdot 1.07^t + 6\sin(t) thousand dollars and satisfies V′′(2)≈−5.33V''(2) \approx -5.33. At t=2t = 2 this says the rate of change of the portfolio is itself

5. Trig mix slope at a quarter turn angle

For f(x)=3cos⁡(x)−2sin⁡(x)+6f(x) = 3\cos(x) - 2\sin(x) + 6, compute f′(π4)f'(\frac{\pi}{4}) rounded to three decimals.

6. Portfolio instantaneous rate

With V(t)=24⋅1.07t+6sin⁡(t)V(t) = 24 \cdot 1.07^t + 6\sin(t) in thousands of dollars, compute V′(2)V'(2) rounded to three decimals.

7. Sine differentiates to cosine everywhere

The formula ddx[sin⁡(x)]=cos⁡(x)\frac{d}{dx}[\sin(x)] = \cos(x) holds for every real number xx.

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