Question

prove that sin^2A +sin^2B+cos^2(A+B) +2sinA.sinB.cos(A+B)=1​

Answer 1

Answer:

Remember these formulas :

•sin2A=2sinAcosA

•cos2A=2cos²A-1=1-2sin²A

•sin²A=(1-cos2A)/2 and cos²A=(1+cos2A)/2

•cos(A+B)=cosAcosB-sinAsinB

•cos(A-B)=cosAcosB+sinAsinB

•cosA+cosB=2cos[(A+B)/2]cos[(A-B)/2]

•2cos(A+B)cos(A-B)=cos2A+cos2B