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Question: Answered & Verified by Expert
If $\sin \alpha+\sin \beta=0=\cos \alpha+\cos \beta$, where $0 < \beta < \alpha < 2 \pi$, then
which one of the following is correct?
MathematicsTrigonometric Ratios & IdentitiesNDANDA 2018 (Phase 1)
Options:
  • A $\quad \alpha=\pi-\beta$
  • B $\alpha=\pi+\beta$
  • C $\quad \alpha=2 \pi-\beta$
  • D $2 \alpha=\pi+2 \beta$
Solution:
2668 Upvotes Verified Answer
The correct answer is: $\alpha=\pi+\beta$
$\sin \alpha+\sin \beta=0=\cos \alpha+\cos \beta$
$\sin \alpha+\sin \beta=0$
$\Rightarrow \sin \alpha=-\sin \beta$
$\Rightarrow \sin \alpha=\sin (\pi+\beta)$
$\Rightarrow \alpha=\pi+\beta$

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