SOLUTION: What is the radius of a cone that has Surface Area of 219.91 in^2 and a slant height of 9 in? I set up the problem: 219.91=(PI)r^2 + 9(PI)r I can't figure out the steps to s

Algebra ->  Surface-area -> SOLUTION: What is the radius of a cone that has Surface Area of 219.91 in^2 and a slant height of 9 in? I set up the problem: 219.91=(PI)r^2 + 9(PI)r I can't figure out the steps to s      Log On


   

Question 732603: What is the radius of a cone that has Surface Area of 219.91 in^2 and a slant height of 9 in?
I set up the problem: 219.91=(PI)r^2 + 9(PI)r
I can't figure out the steps to solve this problem. I think I am missing information?
Answer by KMST(5328) About Me  (Show Source):
You can put this solution on YOUR website!
219.91=%28pi%29r%5E2+%2B+9%28pi%29r --> 219.91%2Fpi=r%5E2+%2B+9r --> 70=r%5E2+%2B+9r (rounding)
70=r%5E2+%2B+9r --> r%5E2+%2B+9r-70=0
You can solve that quadratic equation easily by factoring:
r%5E2+%2B+9r-70=0 --> %28r%2B14%29%28r-5%29=0 --> highlight%28r=5%29 because r=-14 does not make sense.