Question

Prove cos 70°.cos 10° + sin 70°.sin 10° =1÷2

Answer 1

Step-by-step explanation:

Cos 70 . Cos 10 + Sin 70 . Sin 10 = 1/2

LHS:-

This is of the form: Cos A.Cos B + Sin A.Sin B, which is actually Cos ( A-B ).

Here, A = 70, B = 10

Hence we can write it as:

⇒ Cos ( 70 - 10 )  

⇒ Cos 60

Cos 60 is actually 1/2.

Hence LHS = RHS

Hence Proved !!

Answer 2

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