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For the function f(x)=(x+1)2(x−2)2f(x) = (x+1)^2(x-2)^2, which of the following statements are TRUE?

(A) f(x)f(x) is decreasing on (−∞,−1)(-\infty,-1)

(B) f(x)f(x) is increasing on (−1,12)\left(-1,\frac{1}{2}\right)

(C) f(x)f(x) is decreasing on (12,2)\left(\frac{1}{2},2\right)

(D) f(x)f(x) is increasing on (2,∞)(2,\infty)

Choose the correct answer from the options given below:

Solution

✅ Correct Option: 1

f′(x)=2(x+1)(x−2)2+2(x+1)2(x−2)=2(x+1)(x−2)(2x−1)f'(x)=2(x+1)(x-2)^2+2(x+1)^2(x-2)=2(x+1)(x-2)(2x-1).

Critical points are −1, 12, 2-1,\ \frac12,\ 2. Sign of f′f':

x<−1x<-1: (−)(−)(−)<0(-)(-)(-)<0, decreasing.

−1<x<12-1<x<\frac12: (+)(−)(−)>0(+)(-)(-)>0, increasing.

12<x<2\frac12<x<2: (+)(−)(+)<0(+)(-)(+)<0, decreasing.

x>2x>2: all positive, increasing.

All four statements hold.

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