Question

Prove that cos² (45+A) + (45-A)=1​

Answer 1

Cos²(45°—A) + cos²(45°+A)

= [2 cos²(45°—A) + 2 cos²(45°+A)] /2

= [{2 cos²(45°—A)—1} + {2 cos²(45°+A)—1} + 2] /2

= [cos2(45°—A)+cos2(45°+A)+2]/2

= [cos(90°—2A)+cos(90°+2A)+2]/2

= (sin2A—sin2A+2)/2

= 2/2

= 1