Question

cos 65°.cos 25° - sin 65°.sin 25 °

Answer 1

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

cos 65 cos 25- sin 65 sin 25 = cos(65+25)

                                               = cos 90

                                                = 0

Answer 2

Heya mate,Here is ur answer

Cos 65° × cos 25° - sin 65° × sin 25°

= cos (90-25)°×cos 25° - sin (90-25)°×sin 25°

= sin 25° × cos 25° - cos 25° × sin 25°


$sin \: 25 \times \frac{1}{sin \: 25} - cos\: 25\times \frac{1}{cos \: 25}$

= 1-1

= 0

Identities used

⏩Cos(90-A)= sin A

⏩cos A= 1/sinA

⏩Sin =1/cos A

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@Laughterqueen

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