Use the washer method.

y=x^2+2

- All categories
- Pre-Algebra Answers (11,948)
- Algebra 1 Answers (24,265)
- Algebra 2 Answers (10,064)
- Geometry Answers (4,863)
- Trigonometry Answers (2,487)
- Calculus Answers (5,567)
- Statistics Answers (2,831)
- Word Problem Answers (9,106)
- Other Math Topics (5,368)

Consider first the volume of rotation of the inverted U, the superior curve, y=-2x^2+2x+6 for 0<=x<=2. Consider the disc width dx standing on its side with radius y. The volume of the disc is (pi)y^2dx=(pi)(-x^2+2x+6)^2dx. A stack of such discs placed on its side is the volume between the curve and the x axis. So we need to integrate (pi)(x^4-4x^3-8x^2+24x+36)dx for 0<=x<=2. That is, (pi)[x^5/5-x^4-8x^3/3+12x^2+36x] for 0<=x<=2.

Now we have to do the same for the other curve y=x^2+2. The volume of the thin disc is (pi)(x^2+2)^2dx=(pi)(x^4+4x^2+4)dx. This integrates as (pi)[x^5/5+4x^3/3+4x] for 0<=x<=2.

Combine the two volumes by subtracting the latter from the former (inferior from the superior) we get (pi)[-x^4-4x^3+12x^2+32x] for 0<=x<=2. So this evaluates to (pi)(-16-32+48+64)=64(pi)=201.06 cubic units.

...