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Let O be the origin and OX, OY, OZ be th...

Let O be the origin and OX, OY, OZ be three unit vectors in the directions of the sides, QP, RP, QR respectively of a `trianglePQR`.
Q. If the triangle PQR varies, then the minimum value of `cos(P+Q)+cos(Q+R)+cos(R+P)` is

A

`(3)/(2)`

B

`(5)/(3)`

C

`-(5)/(3)`

D

`-(3)/(2)`

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The correct Answer is:
D
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