Trigonometric EquationHard

Question

Let θ, φ, ∈ [0, 2π] be such that 2cos θ (1 - sinφ) = sin2 θ cos φ - 1, tan(2 π - θ) > 0 and - 1 < sin θ < - Then φ cannot satisfy

Options

A.
B.0 < φ <
C.
D. < φ < 2π

Solution

0 cos θ (1 - sin φ) = cosφ- 1 = 2 sin θ cos φ - 1
2 cos θ - 2 cos θ sin φ = 2 sin θ cosφ - 1
2 cos θ + 1 = 2 sin (θ + φ)
tan(π - θ) > 0 ⇒ tan θ < 0 and - 1 < sin θ < -
⇒ θ ∈
< sin (θ + φ) < 1
⇒ 2π + < θ + φ < + 2π
2π + max < φ < 2π + min

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