Trigonometrical Equations 1 Question 10
10. If $0 \leq x<2 \pi$, then the number of real values of $x$, which satisfy the equation
$\cos x+\cos 2 x+\cos 3 x+\cos 4 x=0$, is (2016 Main)
(a) 3
(b) 5
(c) 7
(d) 9
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Answer:
Correct Answer: 10. (c)
Solution:
- Given equation is $\cos x+\cos 2 x+\cos 3 x+\cos 4 x=0$
$\Rightarrow \quad(\cos x+\cos 3 x)+(\cos 2 x+\cos 4 x)=0$
