Solve the following equations :
2 sin2 x = 3 cos x, 0 ≤ x ≤ 2π
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,
2 sin2 x = 3 cos x , 0 ≤ x ≤ 2π
⇒ 2 ( 1 – cos2 x) = 3 cos x
⇒ 2 cos2 x + 3cos x – 2 = 0
⇒ 2 cos2 x + 4 cos x – cos x – 2 = 0
⇒ 2 cos x(cos x + 2) – 1(cos x + 2) = 0
⇒ (2cos x – 1)(cos x + 2) = 0
∴ cos x = �
or cos x = -2 { as cos x lies between -1 and 1 so this value is rejected }
∴ cos x = � = cos π/3
If cos x = cos y, implies x = 2nπ ± y, where n ∈ Z
∴ x = 2nπ ± π/3
But, 0 ≤ x ≤ 2π
∴ x = π/3 and x = 2π - π/3 = 5π/3 ….ans