If cos(a+b)=0, show that sin (a-b)=cos 2b

1.	If cos(a+b)=0, show that sin (a-b)=cos 2b
Answer» Cos(a+b)=0Cosa+cosb=0 Cosa= -cosbWe take rhsSin(a-b)Sina-sinbCos(90-a) -cos(90-b)Cos90-cosa -cos90+cosb-cosa+cosb-(-cosb) + cosbCosb+ cosbCos(b+b)Cos2b prooved Cos(a+b)= 0 (a+b)= 90a=(90-b)Sin(a-b)= sin ( 90-2b)Since, sin (A-B)= sinA* cosB - cosA* sinBSin(90-2b)= sin90cos2b - cos90 -sin2b1cos2b -0*sin2bHence answer is cos2b...... Thank you??

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