Question

Prove that : sin 21°cos 9º - Cos 84° cos 6° = 1/4​

Answer 1

Answer:

Step-by-step explanation:

sin21.cos9-cos84.cos6

=>sin21.cos9-cos(90-6).cos6

=>sin21.cos9-sin6.cos6

=>1/2{2sin21.cos9-2sin6.cos6}

use formula

2sinA.cosB=sin(A+B)+sin(A-B)

=>1/2{sin30+sin12-sin12-sin0}

=>1/2{sin30}

=>1/2 x 1/2=1/4

Answer 2

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1/4 is correct answers...

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