Question

The surface area of a cylinder is 289 cm² and the height is 21 cm. Find the diameter.

Answer 1

\[SA_{cylinder}=2 \pi (\frac{d}{2})^2 + 2 \pi (\frac{d}{2}) h\]Given what you know:\[289cm^2=2 \pi (\frac{d}{2})^2 + 2 \pi (\frac{d}{2}) 21cm\]Now just solve for d.

Answer 2

still dont get it

Answer 3

I gave you the equation with the values filled in. At this point, you just need to solve for d which requires a bit of algebra including a quadratic equation to solve at the end.

At any rate, you should end up with a resulting diameter of ~4cm.