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Mathematics

If 2 cos (A + B) = 2 sin (A - B) = 1; find the values of A and B.

Trigonometric Identities

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Answer

2 cos (A + B) = 1

⇒ cos (A + B) = 12\dfrac{1}{2}

⇒ cos (A + B) = cos 60°

So, A + B = 60° ……………(1)

2 sin (A - B) = 1

⇒ sin (A - B) = 12\dfrac{1}{2}

⇒ sin (A - B) = sin 30°

So, A - B = 30° ……………(2)

Adding equation (1) and (2), we get

(A + B) + (A - B) = 60° + 30°

⇒ A + B + A - B = 90°

⇒ 2A = 90°

⇒ A = 90°2\dfrac{90°}{2}

⇒ A = 45°

From equation (2), A - B = 30°

⇒ 45° - B = 30°

⇒ B = 45° - 30°

⇒ B = 15°

Hence, A = 45° and B = 15°.

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