SOLUTION: let f(x)=x^2+3x and g(x)=2x. If f(n)=28, what is the value of g(n)

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Question 388983: let f(x)=x^2+3x and g(x)=2x. If f(n)=28, what is the value of g(n)
Answer by robertb(5830) About Me  (Show Source):
You can put this solution on YOUR website!
f%28n%29+=+n%5E2+%2B+3n+=+28, or n%5E2+%2B+3n+-+28+=+0.
(n + 7)(n - 4) = 0. Then n = -7 or n = 4. These give g(-7) = 2*-7 = -14, or g(4) = 2*4 = 8.