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NDA 2019
Exam
NDA
Year
2019
Subject
Mathematics
Chapter
Trigonometric Ratios & Identities

NDA 2019 · Mathematics · Trigonometric Ratios & Identities

What is the value of 34^ ^ 236^ ^ - 56^ ^ 124^ ^ 28^ ^ 88^ ^ + 178^...

What is the value of \frac{\sin 34^{{}^{\circ}} \cos 236^{{}^{\circ}}-\sin 56^{{}^{\circ}} \sin 124^{{}^{\circ}}}{\cos 28^{{}^{\circ}} \cos 88^{{}^{\circ}}+\cos 178^{{}^{\circ}} \sin 208^{{}^{\circ}}} ?

Options

  1. A-2
  2. B-1
  3. C2
  4. D1

Correct answer

A. -2

Step-by-step solution

sin⁡34∘cos⁡236∘−sin⁡56∘sin⁡124∘cos⁡28∘cos⁡88∘+cos⁡178∘sin⁡208∘\frac{\sin 34^{{}^{\circ}} \cos 236^{{}^{\circ}}-\sin 56^{{}^{\circ}} \sin 124^{{}^{\circ}}}{\cos 28^{{}^{\circ}} \cos 88^{{}^{\circ}}+\cos 178^{{}^{\circ}} \sin 208^{{}^{\circ}}}=sin⁡34∘(−cos⁡56∘)−sin⁡56∘cos⁡34∘cos⁡28∘sin⁡2∘+cos⁡2∘sin⁡28∘=−sin⁡34∘cos⁡56∘−sin⁡56∘cos⁡34∘sin⁡(28∘+2∘)\begin{aligned} & =\frac{\sin 34^{{}^{\circ}}\left(-\cos 56^{{}^{\circ}}\right)-\sin 56^{{}^{\circ}} \cos 34^{{}^{\circ}}}{\cos 28^{{}^{\circ}} \sin 2^{{}^{\circ}}+\cos 2^{{}^{\circ}} \sin 28^{{}^{\circ}}} \\ & =\frac{-\sin 34^{{}^{\circ}} \cos 56^{{}^{\circ}}-\sin 56^{{}^{\circ}} \cos 34^{{}^{\circ}}}{\sin \left(28^{{}^{\circ}}+2^{{}^{\circ}}\right)}\end{aligned}=−sin⁡(34∘+56∘)sin⁡30∘=−sin⁡90∘sin⁡30∘=−112=−2=-\frac{\sin \left(34^{{}^{\circ}}+56^{{}^{\circ}}\right)}{\sin 30^{{}^{\circ}}}=\frac{-\sin 90^{{}^{\circ}}}{\sin 30^{{}^{\circ}}}=\frac{-1}{\frac{1}{2}}=-2
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