Question

If a, b, c are the angels of a triangle ABC then sin (a+b)=

Answer 1

Answer:

Step-by-step explanation:

In △ABC,

A+B+C=180  degree

B+C=180  degree - A

On dividing both sides by 2, we get,

2 (B+C ) =  2 (180  degree −A )

2 (B+C )=90  degree −  2 A

sin( 2 B+C )=sin(90  degree − 2 A )

sin( 2 B+C )=cos 2 A

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