Verified Solution • 2025–26 Session moderate

QJEEM25Mae358: JEE Main 2025 Mathematics - Class 11 JEEM25Mae358 Solution: The sum of all values of satisfying and is

The sum of all values of θ∈[0,2π]\theta \in[0,2 \pi] satisfying 2sin⁡2θ=cos⁡2θ2 \sin ^2 \theta=\cos 2 \theta and 2cos⁡2θ=3sin⁡θ2 \cos ^2 \theta=3 \sin \theta is

Multiple Choice Options

  • A π\pi
  • B 5π6\frac{5 \pi}{6}
  • C π2\frac{\pi}{2}
  • D 4π4 \pi

Step-by-Step Verified Solution

amp;2sin⁡2θ=cos⁡2θamp;2sin⁡2θ=1−2sin⁡2θamp;4sin⁡2θ=1amp;sin⁡2θ=14amp;sin⁡θ=±12amp;2cos⁡2θ=3sin⁡θamp;2−2sin⁡2θ+3sin⁡θ−2=0amp;(2sin⁡θ−1)(2sin⁡θ−2)=0amp;sin⁡θ=12\begin{aligned}& 2 \sin ^2 \theta=\cos 2 \theta \\& 2 \sin ^2 \theta=1-2 \sin ^2 \theta \\& 4 \sin ^2 \theta=1 \\& \sin ^2 \theta=\frac{1}{4} \\& \sin \theta= \pm \frac{1}{2} \\& 2 \cos ^2 \theta=3 \sin \theta \\& 2-2 \sin ^2 \theta+3 \sin \theta-2=0 \\& (2 \sin \theta-1)(2 \sin \theta-2)=0 \\& \sin \theta=\frac{1}{2}\end{aligned}

so common equation which satisfy both equations is sin⁡θ=12\sin \theta=\frac{1}{2}

θ=π6,5π6(θ∈[0,2π])\theta=\frac{\pi}{6}, \frac{5 \pi}{6} \quad(\theta \in[0,2 \pi])

 Sum =π\text { Sum }=\pi

Related Learning Resources & Exam Preparation