# Math Help - Calculus Problem

1. ## Calculus Problem

2. You are going to be using the formula
$V=\int^b_aA(x)dx$
First see that you are taking the integral from $x=0$ until $x=8$ that is when it intersects the x and y axes.

Now you need to find $A(x)$:
Notice that $x+2y=8$ implies $y=-\frac{1}{2}x+8$.
At $x$ the width of the line perpendicular to the x-axis is then $-\frac{1}{2}x+8$. But this is the diameter of the circle. Thus, its radius is $-\frac{1}{4}x+4$.
The area of this cross section (semicircle) is
$\pi \frac{1}{2}\left(-\frac{1}{4}x+4\right)^2$ (remember the 1/2 it is semi-circle )
Thus,
$V=\pi \int^8_0\frac{1}{2}\left(-\frac{1}{4}x+4\right)^2dx=\pi \cdot 37.\bar 3\approx 116$
I think there is something wrong with your choices.

3. Dear PHckr:

Notice that implies .

Do you see the problem?

Regards,

Rich B.

4. Originally Posted by Rich B.
Dear PHckr: