- #1
Painguy
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Homework Statement
On what intervals is the function f(x) = x^4 − 4x^3 both decreasing and concave up?
x < 0, 2 < x < 3
x < 3
x < 0, x > 2
x > 0, x < -3
2 < x < 3
Homework Equations
The Attempt at a Solution
I tried to get the derivative of f(x) to make it greater than 0
f'(x)=4x^3 -12x^2
0<4x^3-12x^2
0<3x^2(x-3)
o then take 3x^2 to the other side and end up with
0<x-3
3<x
I tried to get the concavity by taking the double derivative of f(x)
f''(x)=12x^2-24x
0<12x^2-24x
0<12x(x-2)
0<x-2
2<x
so the answer is 2<x<3?