Question

what is the formula for the surface area of a cylinder in terms of the radius? (i.e. solve for 'r')

Answer 1

It's \(A=2πrh+2πr2\)

Answer 2

thank you but like i need the equation to equal r

Answer 3

I don't think that's what the question is asking.
When it says in terms of r, it just means to let r represent the radius
It doesn't mean to make it r=...

Answer 4

So that formula^ from Jesse is the correct answer

Answer 5

the actual problem says surface area of cylinder 54(pi) and the height is 6cm, solve in terms of radius, @nikato

Answer 6

What is the formula from Jesse?

So far I have
Area / (2 PI h + 2 PI r) = r
which still leaves an r on both sides

Answer 7

jesse just put the formula for the surface area of a cylinder.. @wolf1728

Answer 8

@kshirley
oh, you should have said that earlier
so you have to plug in 54pi for A and 6 for h in the formula

Answer 9

so
\[54\pi= 2\pi r(6) + 2\pi r ^{2}\]

Answer 10

I thought you need it solved for 'r'
The best I could do is:
h*r + r² = Area / (2 PI)

Answer 11

Here's how to solve it:
http://mathcentral.uregina.ca/QQ/database/QQ.09.10/h/jazmin1.html
Basically, it requires the quadratic formula
where a=1 b=height and c= -1*(Area/(2*PI))

Let's suppose Area = 150.7964473723 sq inches and
height = 5 inches
What is the radius?
a=1 b=5 c=-24


x = (-5 +- sqrt(25 - 4*-24)) / 2*1

x = -5 +- sqrt (25 +96) / 2

x = -5 +(11)/ 2

x = 6/2

radius = 3 which it does !!!

Answer 12

Thanks for the medal!!!

Answer 13

thank you SOOO much!!!

Answer 14

u r welcome :-)