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Example 5:Given that, sin (A + B) = sin A.cos B + cosA.sin B, find the value of sin75 .
Solution :
We have, sin(A + B) = sinAcosB + cosAsinB
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We can write sin 75 = sin (45 + 30 )
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If A = 45 and B = 30 , then, according to the given formula,
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sin (45 + 30 )
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= sin 45 cos 30 + cos 45 sin 30
Example 6:.
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ABC is a right triangle, right angled at C. If A = 60 and AB = 21 units, find the remaining
two sides and B of ABC.
Solution :
cosA =
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cos60 =
7
