a cylinder has a surface area of 339 cm squared. The radius is two times greater than the height. What is the radius of the cylinder? answer to the nearest cm.

Question

anonymous · Answer

You have two pieces of information:

r = 2h (the radius is twice the height)

A = 339 cm^2

The formula for surface area of a cylinder is:

A = (2 * pi * r^2) + (2 * pi * r * h)

Express h in terms of r:

h = r / 2

Substitute that for h:

339 = (2 * pi * r^2) + (2 * pi * r * r/2)

Multiply out the second parentheses:

339 = (2 * pi * r^2) + (pi * r^2)

Simplify:

339 = 3 * pi * r^2

Divide both sides by 3 * pi:

r^2 = 339 / (3 * pi)

Simplify:

r^2 = 113 / pi = 36 (rounded)

r = sqrt(36) = 6 cm

anonymous · Answer

okay. Thanks so much! But where are you getting the 2 from, cause i know its 2 times greater, but still, I dont understand this. can you do a step by step, showing what to do....

anonymous · Answer

That is step by step! hehe :) Medal? :D

anonymous · Answer

yeah, but how would I write that on paper?

dan815 · Answer

lol future u are so funny!!!

anonymous · Answer

haha but I dont get it!!