Application of DerivativeHard

Question

The function f(x) = t(et - 1)(t - 1)(t - 2)3(t - 3)5dt minimum at x equals to

Options

A.0
B.1
C.2
D.3

Solution

f(x) = t(et - 1)(t - 1)(t - 2)3(t - 3)5dt
   
f′(x) t(et - 1)(t - 1)(t - 2)3(t - 3)5dt
= x(ex -1)(x -1)(x - 2)3 (x - 3)5 × 1
   
For local minimum, f′(x) = 0
⇒     x = 0,1, 2,3.
Let f′(x) = g(x) = x(ex - 1)(x - 1)(x - 2)3 (x - 3)5
Using sign scheme rule,
   
This shows that f(x) has a local minimum at x = 1 and x = 3 and maximum at x = 2
Therefore, (b) and (d) are the correct answer.

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