NIMCET 2010 — Mathematics PYQ
NIMCET | Mathematics | 2010f(x)=x22amp;8amp;xamp;2amp;8amp;8amp;x has local maximum at?
Choose the correct answer:
- A.
4
- B.
-4
(Correct Answer) - C.
16
- D.
82−22
-4
Explanation
Solving:
1. Expanding the Determinant:
f(x)=x(x2−16)−8(2x−16)+8(4−2x)
f(x)=x3−16x−16x+128+32−16x
f(x)=x3−48x+160
2. Finding Critical Points:
Differentiate f(x) with respect to x:
f′(x)=3x2−48
Set f′(x)=0:
3x2=48
x2=16⟹x=±4
3. Applying Second Derivative Test:
f′′(x)=6x
-
At x=4:
f''(4) = 6(4) = 24 > 0
So, x=4 is a point of local minimum.
-
At x=−4:
f''(-4) = 6(-4) = -24 < 0
So, x=−4 is a point of local maximum.
Correct Option:
(b) -4
Explanation
Solving:
1. Expanding the Determinant:
f(x)=x(x2−16)−8(2x−16)+8(4−2x)
f(x)=x3−16x−16x+128+32−16x
f(x)=x3−48x+160
2. Finding Critical Points:
Differentiate f(x) with respect to x:
f′(x)=3x2−48
Set f′(x)=0:
3x2=48
x2=16⟹x=±4
3. Applying Second Derivative Test:
f′′(x)=6x
-
At x=4:
f''(4) = 6(4) = 24 > 0
So, x=4 is a point of local minimum.
-
At x=−4:
f''(-4) = 6(-4) = -24 < 0
So, x=−4 is a point of local maximum.
Correct Option:
(b) -4
