The number of solution of cos 2 ⁡ x + cos 2 ⁡ 2 x = 2 in 0,20 is equal to

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Question: Answered & Verified by Expert

The number of solution of

\cos^{2} x + \cos^{2} 2 x = 2

in

[0,20]

is equal to

MathematicsTrigonometric EquationsJEE Main

Solution:

2349 Upvotes Verified Answer

The correct answer is: 7

For this to be true

\cos^{2} x = 1

and

\cos^{2} 2 x = 1

So,

x = n π

Since

x \in [0,20],

n = 0, 1, 2, 3, 4, 5, 6

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