- #1
terryds
- 392
- 13
Homework Statement
What is the volume of a solid formed by the area trapped between y= -x^2 and y= -2x rotated 360° around x-axis?
Homework Equations
V = ∫A(x)dx
The Attempt at a Solution
y=y
-x^2 = -2x
x^2 -2x = 0
x(x-2) = 0
This means that the two functions cross at x = 0 and x = 2
From x = 0 to x = 2 , y = -x^2 will be the upper bound
So, the volume is
## V = \pi \int_{0}^{2}((-x^2)^2-(-2x)^2))dx = \pi \int_{0}^{2}(x^4 - 4x^2)dx = \pi \left [ \frac{1}{5}x^5-\frac{4}{3}x^3 \right ]^2_0 = \pi (\frac{32}{5}-\frac{32}{3})=-4\frac{4}{15}\pi ##
Why do I get negative sign?? What's wrong??