1.

If sinA+sinB=a and cosA+cosB=b, show that cos(A+B) = (b^2-a^2)/(b^2+a^2)

Answer»

SOLUTION :COS(A+B)
=(1-tan^2((A+B)/2)/(1+tan^2((A+B)/2)
= (1-a^2/b^2)/(1+a^2/b^2) = (b^2-a^2)/(b^2+a^2)`


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