Question

If A = 30 degree then show that 4 cos A cos (60-A ) , cos 60 +a = Cos 3 A​

Answer 1

Answer:

cosAcos(60−A)cos(60+A)=

4

cos3A

cos(x−y)cos(x+y)=cos

2

y−sin

2

x

cos3x=4cos

3

x−3cosx

cosAcos(60−A)cos(60+A)

=cosA(cos

2

(A)−sin

2

60)

=cosA(cos

2

A−

4

3

)

=

4

4cos

3

A−3cosA

=

4

cos3A