Q6 of 268 Page 4

If A=60^o and B = 30^o, verify that :
cos (A+B) = cos A cos B – sin A sin B

Given: A=60^o and B =30^o

Now, LHS = Cos (A+B)

⇒ Cos (60 ^o + 30 ^o)

⇒ Cos (90 ^o)

⇒ 0 [∵ cos 90 ^o = 0]

Now, RHS = Cos A Cos B – Sin A Sin B

⇒ cos(60 ^o) cos(30 ^o) – sin(60 ^o) sin (30 ^o)

⇒ 0

∴ LHS = RHS

Hence Proved

Prove the following :

If A=60^o and B = 30^o, verify that :

sin (A – B) = sin A cos B – cos A sin B

If A=60^o and B = 30^o, verify that :

tan (A – B) =

If A=60o and B = 30o, verify that :cos (A+B) = cos A cos B – sin A sin B