# Solve : 3 – 2 cos

Ideas required to solve the problem:

The general solution of any trigonometric equation is given as –

• sin x = sin y, implies x = nπ + (– 1)ny, where n Z.

• cos x = cos y, implies x = 2nπ ± y, where n Z.

• tan x = tan y, implies x = nπ + y, where n Z.

Given,

3 – 2 cos x – 4 sin x – cos 2x + sin 2x = 0

As, cos 2x = 1 – 2sin2 x and sin 2x = 2sin x cos x

3 – 2cos x – 4sin x – (1 – 2sin2 x) + 2sin x cos x = 0

2sin2 x – 4sin x + 2 – 2cos x + 2sin x cos x = 0

2(sin2 x – 2sin x + 1) + 2cos x(sin x – 1) = 0

2(sin x – 1)2 + 2cos x(sin x – 1) = 0

(sin x – 1)(2cos x + 2sin x – 2) = 0

sin x = 1 or sin x + cos x = 1

When, sin x = 1

We have,

sin x = sin π/2

If sin x = sin y, implies x = nπ + (– 1)ny, where n Z

When, sin x + cos x = 1

{ dividing by √2 both sides}

{ }

{ cos A cos B + sin A sin B = cos (A - B)}

If cos x = cos y, implies x = 2mπ ± y, where m Z

Hence,

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