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If 0 lt alpha lt (pi)/(2) and sin alpha ...

If `0 lt alpha lt (pi)/(2) and sin alpha + cos alpha = sqrt2,` then the value of `cos 3 alpha` is-

A

`(1)/(sqrt2)`

B

`-(1)/(sqrt2)`

C

`1/2`

D

`-1/2`

Text Solution

Verified by Experts

The correct Answer is:
B
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