Base of the solid is the area located by the curve. It says cross-sections perpendicular to the x-axis are isosceles right triangles with hypotenuse in the base. I found the upper limit to be 3 and the lower limit to be -3. Can anyone show me how to find the base and the height? I used the 45/45/90 rule and came up with ((144-16x^2)/9)^(1/2)*((2)^(1/2)/2) for the hypotenuse. I know this is wrong, but now really sure how to actually find the base or height.