If θ = 30°, verify that :cos3θ = 4cos3θ – 3cosθ

Given: θ =30oNow, LHS = cos 3(30o)⇒ cos 90o= 0Now, RHS = 4 cos3 θ - 3 cos θ⇒ 4 cos3 (30o) - 3 cos (30o)= 0∴ LHS = RHSHence Proved

Q8 of 268 Page 4

If θ = 30°, verify that :
cos3θ = 4cos³θ – 3cosθ

Given: θ =30^o

Now, LHS = cos 3(30^o)

⇒ cos 90^o

= 0

Now, RHS = 4 cos³ θ - 3 cos θ

⇒ 4 cos³ (30^o) - 3 cos (30^o)

= 0

∴ LHS = RHS

Hence Proved

If A = 30^o, verify that :

cos 2A = 1-2 sin²A=2cos² A – 1

If θ = 30°, verify that :

sin 3θ = 3 sinθ – 4 sin³θ

If sin (A + B) = 1 and cos (A – B) = , then find A and B.

If sin (A + B) = 1 and cos (A – B) = 1, find A and B.