SOLUTION: Let f(x) = x^2 + 18x + 83. On what interval is the function decreasing?

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Question 872968: Let f(x) = x^2 + 18x + 83. On what interval is the function decreasing?
Found 2 solutions by psbhowmick, ewatrrr:
Answer by psbhowmick(878) About Me  (Show Source):
You can put this solution on YOUR website!
f%28x%29+=+x%5E2+%2B+18x+%2B+83
%28df%28x%29%29%2Fdx+=+2x+%2B+18

For f(x) to be decreasing, f'(x) < 0 i.e. 2x+%2B+18+%3C+0 i.e. x < -9

Answer by ewatrrr(24785) About Me  (Show Source):
You can put this solution on YOUR website!
f(x) = x^2 + 18x + 83
f'(x) = 2x + 18 , 2(x+ 9) > 0 when x > -9
decreasing (−∞, -9)