微积分I(标准路径) · free preview

§6.1 Using definite integrals to find area and length (continued)

我们如何利用定积分来度量两条曲线之间的面积?

1. Summary

Summary

2. Sine and cosine over the middle window

Between x=π4x = \frac{\pi}{4} and x=3π4x = \frac{3\pi}{4}, the area between y=sin⁡(x)y = \sin(x) and y=cos⁡(x)y = \cos(x) equals

3. Intersections independent of a parameter

For f(x)=1−x2f(x) = 1-x^2 and g(x)=ax2−ag(x) = ax^2 - a with a>0a \gt 0, the intersection points of the two graphs are

4. Solving for an unknown parameter by area

With f(x)=1−x2f(x) = 1-x^2 above g(x)=ax2−ag(x) = ax^2-a on (−1,1)(-1,1), setting the area between the curves equal to 22 determines aa. The solution is

5. Two sideways parabolas

For the region between x=y(y−2)x = y(y-2) and x=−(y−1)(y−3)x = -(y-1)(y-3), which lies between y=3−32y = \frac{3-\sqrt{3}}{2} and y=3+32y = \frac{3+\sqrt{3}}{2}, the area is 3\sqrt{3}. Report this as a decimal, rounded to three places.

6. A rational slice area

For the region between x=y2−y−2x = y^2-y-2 and x=y+12x = \frac{y+1}{2} on −1≤y≤52-1 \le y \le \frac{5}{2}, the area is 34348\frac{343}{48}. Report this as a decimal, rounded to three places.

7. A fixed intersection window

The curves x=y(y−2)x = y(y-2) and x=−(y−1)(y−3)x = -(y-1)(y-3) intersect at y=3±32y = \frac{3 \pm \sqrt{3}}{2}.

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