Combination of r Things from n Things When All Are Not Different
Let O be the ...
Question
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
centroid
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B
circumcentre
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C
incentre
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D
orthocenter
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Solution
The correct option is D orthocenter −−→OP⋅−−→OQ+−−→OR⋅−−→OS=−−→OR⋅−−→OP+−−→OQ⋅−−→OS⇒−−→OP⋅(−−→OQ−−−→OR)=−−→OS⋅(−−→OQ−−−→OR)⇒(−−→OP−−−→OS)⋅(−−→OQ−−−→OR)=0⇒−→SP⋅−−→RQ=0⇒−→SP⊥−−→RQ Similarly,−−→SR⊥−−→QPand−−→SQ⊥−−→PR Hence, S is the orthocentre of triangle PQR