Let O be the origin and let PQR be an arbitrary triangle. The point S is such that −−→OP⋅−−→OQ+−−→OR⋅−−→OS=−−→OR⋅−−→OP+−−→OQ⋅−−→OS=−−→OQ⋅−−→OR+−−→OP⋅−−→OS
Then the triangle PQR has S as its
A
Circumcentre
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B
Orthocenter
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C
Centroid
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D
Incentre
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Solution
The correct option is B Orthocenter −−→OP⋅−−→OQ+−−→OR⋅−−→OS=−−→OR⋅−−→OP+−−→OQ⋅−−→OS=−−→OQ⋅−−→OR+−−→OP⋅−−→OS −−→OP⋅−−→OQ+−−→OR⋅−−→OS=−−→OR⋅−−→OP+−−→OQ⋅−−→OS ⇒−−→OP⋅(−−→OQ−−−→OR)+−−→OS⋅(−−→OR−−−→OQ)=0
⇒−−→RQ⋅(−−→OP−−−→OS)=→0 ⇒−−→RQ⋅−→SP=→0 ⇒−−→RQ⊥−→SP
and similarly from −−→OR⋅−−→OP+−−→OQ⋅−−→OS=−−→OQ⋅−−→OR+−−→OP⋅−−→OS −−→SR⊥−−→PQ ∴S is the orthocentre.