Mathematics · Trigonometry Ratios and Identities

JEE Main 2026 — 2 April, Morning Shift — Question 30

Let S={x∈[−π,π]:sin⁡x(sin⁡x+cos⁡x)=a,a∈Z}\mathrm{S} = \{\mathrm{x}\in [-\pi ,\pi ]:\sin \mathrm{x}(\sin \mathrm{x} + \cos \mathrm{x}) = \mathrm{a}, \mathrm{a}\in \mathbf{Z}\} . Then n(S)\mathrm{n}(\mathrm{S}) is equal to :

  1. Option A:

    3

  2. Option B:

    6

  3. Option C:

    7

  4. Option D:

    9

    Correct

Answer: D

Step-by-step solution

sin⁡x(sin⁡x+cos⁡x)∈[1−22,1+22]\sin \mathrm{x}(\sin \mathrm{x}+\cos \mathrm{x}) \in\left[\frac{1-\sqrt{2}}{2}, \frac{1+\sqrt{2}}{2}\right] 2 integer will be there ⇒a=0,1\Rightarrow \mathrm{a}=0,1 If a=0sin⁡x(sin⁡x+cos⁡x)=0\mathrm{a}=0 \sin \mathrm{x}(\sin \mathrm{x}+\cos \mathrm{x})=0 ⇒sin⁡x=0\Rightarrow \sin \mathrm{x}=0 \quad or sin⁡x+cos⁡x=0\sin \mathrm{x}+\cos \mathrm{x}=0 x=−π,0,π\mathrm{x}=-\pi, 0, \pi =tan⁡x=−1=\tan \mathrm{x}=-1

3 solutions

x=−π4,3π42 solutions \mathrm{x}=-\frac{\pi}{4}, \frac{3 \pi}{4} 2 \text { solutions }

If a=1sin⁡x(sin⁡x+cos⁡x)=1\mathrm{a}=1 \sin \mathrm{x}(\sin \mathrm{x}+\cos \mathrm{x})=1 sin⁡2x+sin⁡xcos⁡x=1\sin ^{2} \mathrm{x}+\sin \mathrm{x} \cos \mathrm{x}=1 2sin⁡2x+2sin⁡xcos⁡x=22 \sin ^{2} \mathrm{x}+2 \sin \mathrm{x} \cos \mathrm{x}=2 1−cos⁡2x+sin⁡2x=21-\cos 2 \mathrm{x}+\sin 2 \mathrm{x}=2 Sin⁡2x−cos⁡2x=1→\operatorname{Sin} 2 \mathrm{x}-\cos 2 \mathrm{x}=1 \rightarrow square Sin⁡4x=0\operatorname{Sin} 4 \mathrm{x}=0 4x=−4π,−3π4 \mathrm{x}=-4 \pi,-3 \pi, ____\_\_\_\_ 3π,4π3 \pi, 4 \pi x=−π,−3π4,−π2,−π4,0,π4,π2,3π4,π\mathrm{x}=-\pi,-\frac{3 \pi}{4},-\frac{\pi}{2},-\frac{\pi}{4}, 0, \frac{\pi}{4}, \frac{\pi}{2}, \frac{3 \pi}{4}, \pi ⇒x=−3π4,−π2,π4,π2\Rightarrow \mathrm{x}=-\frac{3 \pi}{4},-\frac{\pi}{2}, \frac{\pi}{4}, \frac{\pi}{2} 4 solutions

Total 9 solution

Answer key and solution verified before publishing.

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Exam
JEE Main 2026
Subject
Mathematics
Chapter
Trigonometry Ratios and Identities
Topic
Periodicity of trigometric functions,Solutions of trigonometric equations