Answer:
[tex](cosA + cos B)^2 + (sin A +sinB)^2 \\\\= cos^2A + cos^2B + 2cosA cosB + sin^2A +Sin^2B +2sinAsinB\\\\=(cos^2A + sin^2 A) + (cos^2B +sin^2B) +2cosAcosB + 2sinAsinB\\\\= 1 + 1 + 2cosAcosB + 2sinAsinB\\\\=2 + cos(A+B)+cos(A-B) + cos(A-B) -cos(A+B)\\\\=2 + 2cos(A-B)\\\\=2(1 + cos(A-B))\\\\=2\times 2 cos^2(\frac{A-B}{2})\\\\=4cos^2(\frac{A-B}{2})[/tex]
Hence proved .
