SOLUTION: ok i have ABSOLUTLEY NO CLUE WHAT TO DO I AM SOOO LOST ! PLEASE SOMEONE HELPME!! Find the radius of the right cylinder shown, in which the height of the cylinder is equal to the d

Algebra ->  Bodies-in-space -> SOLUTION: ok i have ABSOLUTLEY NO CLUE WHAT TO DO I AM SOOO LOST ! PLEASE SOMEONE HELPME!! Find the radius of the right cylinder shown, in which the height of the cylinder is equal to the d      Log On


   

Question 566035: ok i have ABSOLUTLEY NO CLUE WHAT TO DO I AM SOOO LOST ! PLEASE SOMEONE HELPME!!
Find the radius of the right cylinder shown, in which the height of the cylinder is equal to the diameter.
ok, soo what i did is find the surface area.
S=2*pi*radius^2+28pi*raduis
so i plugged in the numbers
150pi=2pir^2+2pir(2r)
after that i dont know what todo.. HONESTLEY i dont even think i did it right...
Found 2 solutions by mananth, Edwin McCravy:
Answer by mananth(16946) About Me  (Show Source):
You can put this solution on YOUR website!
150pi=2pir^2+2pir(r)
I presume 150 pi is the surface area
150pi=2pir^2+2pir^2
150pi=4pir^2
divide by 4pi
37.5=r^2
r= sqrt(37.5)
r=6.12

Answer by Edwin McCravy(20054) About Me  (Show Source):
You can put this solution on YOUR website!
ok i have ABSOLUTLEY NO CLUE WHAT TO DO I AM SOOO LOST ! PLEASE SOMEONE HELPME!!
Find the radius of the right cylinder shown, in which the height of the cylinder is equal to the diameter. 

Think of a tin can.

Surface area = circumference*height + area of the top circle + area of the bottom circle

     |       |        |         |   |            |           |               |            

     S       =    (2*pi*r) *   h   +          pi*rē         +             pi*rē

           S+=+2%2Api%2Ar%2Ah+%2B+2pi%2Ar%5E2

           S+=+2%2Api%2Ar%28h+%2B+r%29

Since the height equals the diameter, and the diameter equals twice the radius,

the height equals twice the radius, so substitute 2r for h

           S+=+2%2Api%2Ar%282r+%2B+r%29

           S+=+2%2Api%2Ar%283r%29

           S+=+6%2Api%2Ar%5E2
         
Substitute 150pi for S

           150pi+=+6%2Api%2Ar%5E2

Divide both sides by 6%2Api

           %28150pi%29%2F%286%2Api%29+=+r%5E2

The pi's cancel on the left and 6 divided into 150 is 25

              25+=+r%5E2

              sqrt%2825%29+=+r

              5+=+r

Edwin