SOLUTION: interval does increase y=x^4+4x

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Question 765891: interval does increase y=x^4+4x
Answer by tommyt3rd(5050) About Me  (Show Source):
You can put this solution on YOUR website!
%0D%0Ady%2Fdx=4x%5E3%2B4=4%28x%2B1%29%28x%5E2-x%2B1%29%0D%0A
when x=-2
dy%2Fdx=4%28-1%29%284-2%2B1%29=-12
so y decreases on (-oo, -1)
and thus increases on (-1,oo)

:)