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If cos(theta-alpha),costheta,cos(theta+a...

If `cos(theta-alpha),costheta,cos(theta+alpha)` are in H.P.,then `costhetasec(alpha//2)` is equal to

A

`-1`

B

`pmsqrt2`

C

`pm2`

D

`pm3`

Text Solution

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The correct Answer is:
B
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