Q.24. In PQR; if sec R = 2 sin Q cosec P, then PQR is
A. an isosceles triangle
B. an equilateral triangle
C. a right-angled triangle  
D. a right-angled isosceles triangle


sec R=2 sin Q cosec P1cos R=2 sin Qsin PBy sine rulepsin P=qsin Q=rsin Rsin Qsin P=qpBy cosine rulecos R=p2+q2-r22pq1p2+q2-r22pq=2 qp2pqp2+q2-r2=2 qppp2+q2-r2=1pp2+q2-r2=p2q2=r2q=rHence it is an isosceles triangle
 

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