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Questions  

If O is the origin and Px1,y1,Qx2,y2 are two points, then OP.OQ cosPOQ

a
x1x2+y/1y2
b
x1y2+x2y1
c
x1    y2    −x2    y1
d
none of these

detailed solution

Correct option is A

Using cosine formula in ∆POQ we havePQ2=OP2+OQ2−2OP×OQcos⁡∠POQ⇒ x1−x22+y1−y22=x12+y12+x22+y22−2OP×OQcos⁡∠POQ⇒OP⋅OQcos⁡∠POQ=x1x2+y1y2

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