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sunny chawla Grade:
        


If    a/SinA = b/CosA   then prove that   SinACosA = ab/a2 + b2


7 years ago

Answers : (1)

AskiitiansExpert Abhinav Batra
25 Points
										

Dear sunny


 


we know by sine rule that


a/sinA=b/sinB=c/sinC


 


futher it is given that


a/sinA=b/cosA


hence b/sinB=b/cosA


So cosA=sinB


cosA=cos(90-B)


hence A+B=90


So C=90


Suppose 


a/sinA=b/sinB=c/sinC=k


sinA=a/k;sinB=b/k;sinC=c/k


so sinA sinB/sin2 C=ab/c2


but we know Sin B =Cos A and c2=a2 +b2 and SinC=1 (since triangle is right angled at C)


so sin A cosA=ab/a2 + b2


 


ALL THE BEST


Abhinav Batra

7 years ago
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