Question

cos35 . cos25 - cos55 . cos65=?

Answer 1

cos 35 cos 25 - cos 55 cos 65
= cos 35 cos 25 - sin(90-55) sin (90-65)
= cos 35 cos 25 - sin 35 sin 25
= cos ( 35 + 25)°
= cos ( 60°)
= 1/2

cos A cos B - sin A sin B = cos ( A+B)

Answer 2

Answer:

Cos 35 cos 25 - cos 55 cos 65

= cos 35 cos 25 - sin(90-55) sin (90-65)

= cos 35 cos 25 - sin 35 sin 25

= cos ( 35 + 25)°

= cos ( 60°)

= 1/2

cos A cos B - sin A sin B = cos ( A+B)