math homework ftl .. *help*

[RAGEQUiT]

hey guys,
im struggling with my math homework for like 3 hours.
I cant get it right so i would be great if you could help me with it
->

A cone has a surface of O=628 cm² and a sideline of s=12.4 cm.
Calculate the radius of Base circle.
Do that with a quadratic equation.

so what i did allready :

I used the formula for the surface O and transformed it.
Pi * r² + 12,5 * r * Pi = 628

But what I need to do now is to transform it into an "pq-formula"
and i just dont know how to do that.

well i tried :
Pi * r2 + 12,5r * Pi - 628 = 0
but that wont work later on.

thx for future help

[RAGEQUiT]

That's honestly your first post here? not sure you understand this community...

well, I do understand this community KS.
I thought I dont need to introduce myself as I was a part of it a while ago.

[RAGEQUiT]

Think you'd better introduce yourself. And why would you post it here of all places?

Ok, Im R4d0xZz and I know that I suck and stuff but I changed alot.
I know I did shit to the community especially to ultra.
I cant do more then appologize.

however. I choose this place because you guys are nice and smart and I know you guys can handle that question.
KS please unban my old acc. because I would like to post on this forum again.

[Infinite]

A cone has a surface of O=628 cm² and a sideline of s=12.4 cm.
Calculate the radius of Base circle.
Do that with a quadratic equation.

SA = πrs + πr^2, therefore 628 = 12.4πr + πr^2 and with a bit of rearranging 0 = πr^2 + 12.4πr - 628.

use the quadratic ((-b (+/-) √(b^2 - 4ac))/(2a)) to find that r = 9.238, -21.638 (or just 9.238 cm, since the radius cannot be negative).

Pi * r2 + 12,5r * Pi - 628 = 0
but that wont work later on.

Why not?

Is the side length 12.5 or 12.4? you posted 12.4, as I quoted at first, but then used 12.5 later on. If it's 12.5, the radius is 9.208 cm

[RAGEQUiT]

the radius was 12.5 sorry.
I got it now.

thanks infinite