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JEE Advanced 2010Paper 1
Exam
JEE Advanced
Year
2010
Paper
Paper 1
Subject
Mathematics
Chapter
Trigonometric Equations

JEE Advanced 2010 · Paper 1 · Mathematics · Trigonometric Equations

The number of all possible values of θ , where 0 θ π , for which...

The number of all possible values of θ\theta, where 0<θ<π0 \lt \theta \lt \pi, for which the system of equations (y+z)cos⁡3θ=(xyz)sin⁡3θxsin⁡3θ=2cos⁡3θy+2sin⁡3θz\begin{array}{r} (y+z) \cos 3 \theta=(x y z) \sin 3 \theta\\ x \sin 3 \theta=\frac{2 \cos 3 \theta}{y}+\frac{2 \sin 3 \theta}{z} \end{array}and (xyz)sin⁡3θ=(y+2z)cos⁡3θ+ysin⁡3θ(x y z) \sin 3 \theta=(y+2 z) \cos 3 \theta+y \sin 3 \theta have a solution (x0,y0,z0)\left(x_0, y_0, z_0\right) with y0z0≠0\quad y_0 z_0 \neq 0, is

Correct answer

3

Step-by-step solution

Given equations can be written as xsin⁡3θ−cos⁡3θy−cos⁡3θz=0xsin⁡3θ−2cos⁡3θy−2sin⁡3θz=0 and xsin⁡3θ−2ycos⁡3θ−1z(cos⁡3θ+sin⁡3θ)=0Eqs.(ii)and(iii),implies\begin{gathered}x \sin 3 \theta-\frac{\cos 3 \theta}{y}-\frac{\cos 3 \theta}{z}=0 \\ x \sin 3 \theta-\frac{2 \cos 3 \theta}{y}-\frac{2 \sin 3 \theta}{z}=0 \\ \text{ and }x \sin 3\theta-\frac{2}{y} \cos3 \theta\\ -\frac{1}{z}(\cos3 \theta+\sin3 \theta)=0 \end{gathered} Eqs. (ii) and (iii), implies2sin⁡3θ=cos⁡3θ+sin⁡3θ⇒sin⁡3θ=cos⁡3θ∴tan⁡3θ=1⇒3θ=π4,5π4,9π4 or θ=π12,5π12,9π12.\begin{aligned}& 2 \sin 3 \theta=\cos3 \theta+\sin3 \theta\\ \Rightarrow & \sin 3 \theta=\cos3 \theta\\ \therefore & \tan 3 \theta=1 \\ \Rightarrow & 3 \theta=\frac{\pi}{4}, \frac{5 \pi}{4}, \frac{9 \pi}{4} \text{ or } \theta=\frac{\pi}{12}, \frac{5 \pi}{12}, \frac{9 \pi}{12} . \end{aligned}$$
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