a cylinder has a surface area of 402 cm^2. The height is three times greater than the radius. What is the height of the cylinder?

Question

what i did:

402 = 2πr^2+2πr(3r)

how do i separate r? 

Answer 1

2π r² + 2π r(3r) = 2π r² + 6π r² = 8π r². I hope this helped, and if you need more assistance, I or another tutor will be happy to help.

Answer 2

Nice start, Mathalina!!! Next, you have to simplify equation, you wrote, and solve it for "r"

2(pi)r² + 2(pi)r(3r) = 402
2(pi)r² + 6(pi)r² = 402
8(pi)r² = 402
pi = 22/7
r² = (402/8) · (7/22)
r ≈ √15.99 = 3.0 (we use only positive value of the square root, distance cannot be negative)
h = 3r ≈ 9.0 cm

Answer 3

2∏rh + 2∏r² = 402

h = 4r

2∏r(4r) + 2∏r² = 402

8∏r² + 2∏r² = 402

10∏r² = 402

r² = 402/10∏

r = √402/√10∏

h = (4√402)/√(10∏)