Skip to main content
Back to Trigonometric Equations
JEE Main 2024
Trigonometric Equations
Trigonometric Equations
Medium

Question

If θϵ[7π6,4π3]\theta \epsilon\left[-\frac{7 \pi}{6}, \frac{4 \pi}{3}\right], then the number of solutions of 3cosec2θ2(31)cosecθ4=0\sqrt{3} \operatorname{cosec}^2 \theta-2(\sqrt{3}-1) \operatorname{cosec} \theta-4=0, is equal to :

Options

Solution

To find the solutions of the equation 3cosec2θ2(31)cosecθ4=0\sqrt{3} \operatorname{cosec}^2 \theta - 2(\sqrt{3} - 1) \operatorname{cosec} \theta - 4 = 0, we can begin by solving for cosecθ\operatorname{cosec} \theta. The quadratic equation in terms of cosecθ\operatorname{cosec} \theta is: 3cosec2θ2(31)cosecθ4=0\sqrt{3} \operatorname{cosec}^2 \theta - 2(\sqrt{3} - 1) \operatorname{cosec} \theta - 4 = 0 Using the quadratic formula: cosecθ=232±(2(31))2+43423\operatorname{cosec} \theta = \frac{2\sqrt{3} - 2 \pm \sqrt{(2(\sqrt{3} - 1))^2 + 4 \sqrt{3} \cdot 4}}{2\sqrt{3}} Simplifying inside the square root: (2(31))2+434=4(3+123)+163(2(\sqrt{3} - 1))^2 + 4\sqrt{3} \cdot 4 = 4(3 + 1 - 2\sqrt{3}) + 16\sqrt{3} This simplifies to: 4(423)+163=1683+163=16+834(4 - 2\sqrt{3}) + 16\sqrt{3} = 16 - 8\sqrt{3} + 16\sqrt{3} = 16 + 8\sqrt{3} Therefore, the quadratic gives: cosecθ=232±2(3+1)23\operatorname{cosec} \theta = \frac{2\sqrt{3} - 2 \pm 2(\sqrt{3} + 1)}{2\sqrt{3}} By solving, we find: cosecθ=23,2\operatorname{cosec} \theta = \frac{-2}{\sqrt{3}}, 2 Thus, for each value of the cosecant, θ\theta can take several values that fall within the given interval [7π6,4π3][- \frac{7\pi}{6}, \frac{4\pi}{3}]: θ=7π6,2π3,π3,π6,5π6,4π3\theta = \frac{-7\pi}{6}, \frac{-2\pi}{3}, \frac{-\pi}{3}, \frac{\pi}{6}, \frac{5\pi}{6}, \frac{4\pi}{3} These are all the possible solutions for θ\theta within the defined range.

Practice More Trigonometric Equations Questions

View All Questions