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Trigonometry – II — Maths STD 11 Science — Question

Maharashtra BoardEnglish MediumSTD 11 ScienceMathsTrigonometry – II2 Marks
MCQ
If $8 \theta=\pi$, then $\cos 7 \theta+\cos \theta$ is equal to
  • ✓
    $0$
  • B
    1
  • C
    -1
  • D
    7
✓

Answer

Correct option: A.
$0$
(A)
$\cos 7 \theta+\cos \theta=\cos (8 \theta-\theta)+\cos \theta$
$=\cos (\pi-\theta)+\cos \theta$ $\ldots[\because 8 \theta=\pi($ given $)]$
$=-\cos \theta+\cos \theta=0$

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