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

Question

shane_b · Answer

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

anonymous · Answer

still dont get it

shane_b · Answer

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.