Find the intervals on which each of the following functions is (a) increasing (b) decreasing.
f(x)=x4-4x3+4x2+15
f’(x)=4x3-12x2+8x
= 4x(x2-3x+2)
=4x(x-1)(x-2)
Function f(x) is decreasing for x ∈ (-∞,0] ∪ [1, 2] and increasing in x ∈ (0,1) ∪ (2, ∞)
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