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JEE Main 2018
Inverse Trigonometric Functions
Inverse Trigonometric Functions
Hard

Question

Let the inverse trigonometric functions take principal values. The number of real solutions of the equation 2sin1x+3cos1x=2π52 \sin ^{-1} x+3 \cos ^{-1} x=\frac{2 \pi}{5}, is __________.

Answer: 2

Solution

2sin1x+3cos1x=2π5π2+cos1x=2π5cos1x=2π5π2cos1x=π10\begin{aligned} & 2 \sin ^{-1} x+3 \cos ^{-1} x=\frac{2 \pi}{5} \\ & \frac{\pi}{2}+\cos ^{-1} x=\frac{2 \pi}{5} \\ & \cos ^{-1} x=\frac{2 \pi}{5}-\frac{\pi}{2} \\ & \cos ^{-1} x=\frac{-\pi}{10} \end{aligned} Which is not possible as cos1x[0,π]\cos ^{-1} x \in[0, \pi] \therefore \quad No solution

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