Question

The value of Cos 80 cos 2
0 + sin 80 sin 20​

Answer 1

Find The Value of:-

Cos 80 cos 20 + sin 80 sin 20

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Formula(Identity) to be used:→

Cos ( x + y ) = cos x.cos y - sin x.sin y

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✏️✏️SOLUTION→

Taking the Identity,

Cos ( x + y ) = cos x.cos y - sin x.sin y

Substitute the y with - y,

We get,

Cos ( x - y ) = cos x.cos y + sin x.sin y.

Now,this new IDENTITY is same as Given Question.

therefore,

On taking 80° as X and 20° as Y.

We Get,

➠Cos 80 cos 20 + sin 80 sin 20 = Cos( 80° + 20° )

Hence,

→Cos ( 80° + 20° )

→Cos 100° or Sin 10°. ✒️ ANSWER.✒️

Answer 2

Step-by-step explanation:

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