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The equation cos^8x+bcos^4x+1=0 will hav...

The equation `cos^8x+bcos^4x+1=0` will have a solution if `b` belongs to `(-oo,2]` (b) `[2,oo]` (c) `[-oo,-2]` (d) none of these

A

`(-oo, 2]`

B

`[2, oo)`

C

`(-oo, -2]`

D

none of these

Text Solution

Verified by Experts

The correct Answer is:
C
`cos^(8)x+b cos^(4) x+1=0`
`rArr b=-(cos^(4) x+1/(cos^(4) x)) le -2 AA x in R`
`rArr b in (-oo, -2]`
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