Question

Please proved it immediately ​

Answer 1

Answer:

W.K.T,

sin A sin B + cos A cos B = cos(A-B)

sin (nA+A) sin(nA+2A) + cos(nA+A) cos(nA+2A) = cos (nA+A-nA-2A) = cos (-A) = cos A

Hence proved

Hope it helps you

Answer 2

Answer:

Here is your proof. Hope you liked it!

Step-by-step explanation:

Taking Left hand side,

We know that,

Cos ( A - B ) = Cos A . Cos B + Sin A . Sin B

A = ( n + 1 ) A

B = ( n + 2 ) A

So, = Cos  [( n + 1 ) A - ( n + 2 ) A )  

= Cos ( n  + A - n A - 2 A )  

= Cos ( - x )

= Cos x { Since cos(-x) = Cos x }

Hence proved.

LHS = RHS