Question

cos 180° = cos² 90° - sin² 90°

Answer 1

Answer:

= cos²(90-a) +cos²(180-a)

= cos²(90-a)+cos(180-a) x  cos(180-a)

= cos²(90-a) + sin²(90-(180-a))

= cos²(90-a)+sin²(90-a)

= 1

hope this helps you