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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) +18 x +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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