

InterviewSolution
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Sin (A + B) = Sin A + Sin B is true forA) A = 30°; B = 60° B) A = 30°; B = 45° C) A = 45°; B = 60° D) None of these |
Answer» Correct option is: D) None of these (A) A = \(30^\circ\) and B = \(60^\circ\) = A + B = \(30^\circ\) + \(60^\circ\) = \(90^\circ\) Now, sin A + sin B = sin \(30^\circ\) + sin \(60^\circ\) = \(\frac 12\) + \(\frac {\sqrt3}{2}\) = \(\frac {1+\sqrt3}{2} >1\) But sin (A +B) = sin \(90^\circ\) = 1 Hence, sin A + sin B \(\neq\) sin (A+B) (B) A = \(30^\circ\), B = \(45^\circ\) \(\therefore\) A + B = \(30^\circ\) + \(45^\circ\) = \(75^\circ\) Now, sin A + sin B = sin \(30^\circ\) + sin \(45^\circ\) = \(\frac 12\) + \(\frac 1{\sqrt2}\) = \(\frac {1+\sqrt2}2 > 1\) But sin (A+B) = sin \(75^\circ\) < 1 (\(\because\) -1 \(\leq\) sin \(\theta\) \(\leq\)1) Hence, sin (A+B) \(\neq\) sin A + sin B (C) A = \(45^\circ\), B = \(60^\circ\) \(\therefore\) A + B = \(45^\circ\)+\(60^\circ\) = \(105^\circ\) Nw, sin A + sin B = sin \(45^\circ\) + sin \(60^\circ\) = \(\frac 1{\sqrt2}\) + \(\frac {\sqrt3}{2}\) = \(\frac {\sqrt2+\sqrt3}{2}\) >1 But sin (A+B) = sin \(105^\circ\) < 1 ( \(\because\) -1 \(\leq\) sin \(\theta\) \(\leq\) 1) Hence, sin A + sin B \(\neq\) sin (A+B) Correct option is: D) None of these |
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