Q41 / 90 · JEE Main 2023 (25 Jan Shift 2) · Mathematics

Let the function f(x)=2x3+(2p-7)x2+3(2p-9)x-6 have a maxima for some value of x<0 and a minima for some value of x>0. Then, the set of all values of p is

  • A
    92,∞
  • B
    0,92
  • Correct answer
    C
    -∞,92
  • D
    -92,92

Solution

Given,f(x)=2x3+(2p-7)x2+3(2p-9)x-6

On taking differentiation w.r.t x, we get

f'(x)=6x2+2(2p-7)x+3(2p-9)

⇒f'(0)=6(0)2+2(2p-7)(0)+3(2p-9)

⇒f'(0)=3(2p-9)

Here, given that for x<0 the function has maxima and for x>0 the function has minima so the function is decreasing function about x=0,

Hence f'(0)<0

So, 3(2p-9)<0

⇒p<92

Therefore, p∈-∞,92

Hence, the correct answer is option: 'C'.

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