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NDA 2020
Exam
NDA
Year
2020
Subject
Mathematics
Chapter
Trigonometric Ratios & Identities

NDA 2020 · Mathematics · Trigonometric Ratios & Identities

Paragraph: Read the following information and answer: Let α=β=15^ ^...

Paragraph: Read the following information and answer: Let α=β=15∘\alpha=\beta=15^{{}^{\circ}}.
Question: What is sin⁡(α+1∘)+cos⁡(β+1∘)equalto?\sin \left(\alpha+1^{{}^{\circ}}\right)+\cos \left(\beta+1^{{}^{\circ}}\right) equal to?

Options

  1. A3cos⁡1∘+sin⁡1∘\sqrt{3} \cos 1^{{}^{\circ}}+\sin 1^{{}^{\circ}}
  2. B3cos⁡1∘−12sin⁡1∘\sqrt{3} \cos 1^{{}^{\circ}}-\frac{1}{2} \sin 1^{{}^{\circ}}
  3. C12(3cos⁡1∘+sin⁡1∘)\frac{1}{\sqrt{2}} \left(\sqrt{3} \cos1^{{}^{\circ}}+\sin 1^{{}^{\circ}}\right)
  4. D12(3cos⁡1∘+sin⁡1∘)\frac{1}{2} \left(\sqrt{3} \cos1^{{}^{\circ}}+\sin 1^{{}^{\circ}}\right)

Correct answer

C. 12(3cos⁡1∘+sin⁡1∘)\frac{1}{\sqrt{2}} \left(\sqrt{3} \cos1^{{}^{\circ}}+\sin 1^{{}^{\circ}}\right)

Step-by-step solution

sin⁡(α+1∘)+cos⁡(β+1∘)=2{12⋅sin⁡(α+1∘)+12⋅cos⁡(β+1∘)}\sin \left(\alpha+1^{{}^{\circ}}\right)+\cos \left(\beta+1^{{}^{\circ}}\right)=\sqrt{2}\left\{\frac{1}{\sqrt{2}} \cdot \sin \left(\alpha+1^{{}^{\circ}}\right)+\frac{1}{\sqrt{2}} \cdot \cos \left(\beta+1^{{}^{\circ}}\right)\right\}=2{cos⁡45∘⋅sin⁡(α+1)+sin⁡45∘⋅cos⁡(α+1)}(∵α=β)\begin{aligned}=\sqrt{2}\left\{\cos 45^{{}^{\circ}} \cdot \sin (\alpha+1)+\sin 45^{{}^{\circ}} \cdot \cos (\alpha+1)\right\} & \\ & (\because \alpha=\beta)\end{aligned}$\begin{aligned} & =\sqrt{2}\left\{\sin \left(\alpha+1+45^{{}^{\circ}}\right)\right\}=\sqrt{2} \cdot \sin \left(15^{{}^{\circ}}+1^{{}^{\circ}}+45^{{}^{\circ}}\right) \\ & =\sqrt{2} \cdot \sin 61^{{}^{\circ}} (i) \end{aligned} Again 12(3⋅cos⁡1∘+sin⁡1∘)=22(32⋅cos⁡1∘+12sin⁡1∘)=2⋅(sin⁡60∘⋅cos⁡1∘+cos⁡60∘⋅sin⁡1∘)=2(sin⁡61∘)(ii) Thus ( i )=( ii )\begin{aligned} & \frac{1}{\sqrt{2}}\left(\sqrt{3} \cdot \cos 1^{{}^{\circ}}+\sin 1^{{}^{\circ}}\right) \\ & =\frac{2}{\sqrt{2}}\left(\frac{\sqrt{3}}{2} \cdot \cos 1^{{}^{\circ}}+\frac{1}{2} \sin 1^{{}^{\circ}}\right) \\ & =\sqrt{2} \cdot\left(\sin 60^{{}^{\circ}} \cdot \cos 1^{{}^{\circ}}+\cos 60^{{}^{\circ}} \cdot \sin 1^{{}^{\circ}}\right) \\ & =\sqrt{2}\left(\sin 61^{{}^{\circ}}\right) (ii) \\ & \text{ Thus }(\text{ i })=(\text{ ii }) \end{aligned}\frac{1}{\sqrt{2}} \left(\sqrt{3} \cdot \cos1^{{}^{\circ}}+\sin 1^{{}^{\circ}}\right)$.
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