Question
The function f(x) = 2x3 - 15x2 + 36x + 4 is maximum at x =
- 3
- 0
- 4
- 2
2
Soluctio :
Given, f(x) = 2x3 - 15x2 + 36x + 4
lmplies that f'(x) = 6x2 - 30x + 36
For a local maxima or a local minima, we must have f'(x) = 0
lmplies that 6x2 - 30x + 36 = 0
lmplies that x2 - 5x + 6 = 0
(x - 2)(x - 3) = 0
lmplies that x = 2, 3
Now, f''(x) = 12x - 30
lmplies that f''(2) = 24 - 30 = 6 < 0
Therefore, x = 1 is a local maxima.
Also, f''(3) = 36 - 30 = 6 > 0
Therefore, x = 2 is a local maxima.
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