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The point of local maxima of the function f(x)=(x−2)5(x+2)2f(x) = (x - 2)^5(x + 2)^2 is

Solution

✅ Correct Option: 4

Given f(x)=(x−2)5(x+2)2f(x) = (x - 2)^5(x + 2)^2

To find critical points, find the first derivative using the product rule:

Let u=(x−2)5u = (x - 2)^5 and v=(x+2)2v = (x + 2)^2

u′=5(x−2)4u' = 5(x - 2)^4

v′=2(x+2)v' = 2(x + 2)

f′(x)=5(x−2)4(x+2)2+(x−2)5⋅2(x+2)f'(x) = 5(x - 2)^4(x + 2)^2 + (x - 2)^5 \cdot 2(x + 2)


Factor out the common terms (x−2)4(x - 2)^4 and (x+2)(x + 2):

f′(x)=(x−2)4(x+2)[5(x+2)+2(x−2)]f'(x) = (x - 2)^4(x + 2)[5(x + 2) + 2(x - 2)]

f′(x)=(x−2)4(x+2)[5x+10+2x−4]f'(x) = (x - 2)^4(x + 2)[5x + 10 + 2x - 4]

f′(x)=(x−2)4(x+2)(7x+6)f'(x) = (x - 2)^4(x + 2)(7x + 6)


Set f′(x)=0f'(x) = 0:

(x−2)4(x+2)(7x+6)=0(x - 2)^4(x + 2)(7x + 6) = 0

Critical points are:

x=2x = 2

x=−2x = -2

x=−67x = -\dfrac{6}{7}


Apply the first derivative test. Note that (x−2)4(x - 2)^4 is always positive.

For x<−2x < -2, test x=−3x = -3:

(x+2)<0(x + 2) < 0 and (7x+6)<0(7x + 6) < 0, so f′(x)>0f'(x) > 0 (increasing)

For −2<x<−67-2 < x < -\dfrac{6}{7}, test x=−1x = -1:

(x+2)>0(x + 2) > 0 and (7x+6)<0(7x + 6) < 0, so f′(x)<0f'(x) < 0 (decreasing)

At x=−2x = -2, the function changes from increasing to decreasing.

Therefore, x=−2x = -2 is a local maximum.

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