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Questions  

In  a  ΔPQR,  if  3sinP+4cosQ=6  and  4sinQ+3cosP=1then the acute angle Ris equal to 

a
π6
b
5π6
c
3π4
d
π4

detailed solution

Correct option is A

We have 3sinP+4cosQ=6, 4sinQ+3cosP=1. Squaring on both sides and adding, we get 9sin2P+cos2P+16sin2Q+cos2Q+24sinPcosQ+cosPsinQ=37 ⇒24sinP+Q=37-25=12 ⇒sinπ-R=12  ∵P+Q+R=π ⇒sinR=12 ⇒R=π6∵R is acute

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