Question

prove that cos 65 cos 25 -sin 65 sin 25=0​

Answer 1

cos65 cos25 - sin 65 sin 25 =0
cos (65-90) cos 25 - sin (65-25) sin25= 0
sin25 cos 25 - sin (65-25) sin25 =0
0=0

Answer 2

Answer:

• We know that cosA cosB-sinA sinB =cos(A+B)
• Applying this formula we get,

LHS:

Cos65 cos25-sin 65 sin 25=cos(65+25)

=cos(90)

=0

=RHS

hence proved