Question

( cos x + cosy)² + (sin x - sin y ) ^2 = 4 cos ^2 x+y /2 ​

Answer 1

Step-by-step explanation:

cos²x+cos²y+2cosxcosy+sin²x+sin²y-2sinxsiny

cos²x+sin²x+cos²y+sin²y+2cosxcosy-2sinxsiny

2+2cosxcosy-2sinxsiny

2[1+cos(x+y)]

2[1+2cos²(x+y/2)-1]---------{cos2a=2cos²a-1}

4cos²(x+y/2)