Question

Verify cos3A=4Cos3A-3cosA when A=30°​

Answer 1

Answer:

If A =30

∘

cos3A=Acos

3

A−3cosA

cos90

∘

=4(cos30

∘

)

2

−3(cosA30

∘

)

0=4.(

2

3

)=

2

3.

3

0=4.

2×2×2

3

3

−

2

3

3

0=

2

3

3

−

2

3

3

0 =0

LHS = RHS

Hence proved