Need to find this out for test tommorow?

Question

If you have a cylinder and all it gave you was the height and the area of the top circle so an example

A=81Pie
H=7


Also how do i find the Surface area and volume of a triangular prism? i think its just 1/2 l*w*h? am i wrong?
How would i find the radius of this circle to find out the area or the surface area?


Also...

If i have the circumfrence and the height as well so example



C=81pie
H=7

Would the diameter just be 81 then sice c=d*pie?

Please help? lol and thanks

Answer 1

The surface area of a cylinder is its lateral area plus the two end areas
S = 2πr^2 + 2πrh = 2πr(r + h)
In this case S = 2*81π + 2*9*7π = 288π
The volume of a cylinder isthe area of it's end times its height,
V = Ah = πr^2h
V = 7*81π = 567π

You have the formula for the volume of a triangular prism right.
The surface area is a little tougher. For that you need the lengths of all 3 sides of the triangular faces. Call the side lengths w, x, and y. Then
S = 2(1/2)w*h + lw + lx + ly

C = πd, so if C = 81π, d must be 81