Q4 of 29 Page 8

If A, B and C are interior angles of a triangle ABC, then show that

[CBSE 2008]

To Prove: 



Proof:

We know, By angle sum property of a triangle

∠A + ∠B + ∠C = 180°

⇒ B + C = 180°- A

Taking sin on both sides of equation

Therefore,



As, sin(90 - θ) = cos θ

Therefore, 

Hence proved

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