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The interval on which f(x)=2x^(3)+9x^(2)...

The interval on which `f(x)=2x^(3)+9x^(2)+12x-1` is decreasing in

A

`(-1,oo)`

B

`(-2,-1)`

C

`(-oo,-2)`

D

`(-1,1)`

Text Solution

Verified by Experts

The correct Answer is:
B
`f(x) = 2x^3 + 9x^2 + 12 -1`
`f.(x) = 6x^2 + 18x + 12`
For decreasing
`f.(x) lt 0`
`6x|+18x +12 lt 0`
`x^2 + 3x + 2 lt 0`
`(x+1) (x+2) lt 0`
`x in (-2,-1)`
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