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Maths Question 13 – JEE-MAIN 2026

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If sin⁡(tan−1⁡(x2))=cot⁡(sin−1⁡1−x2), x∈(0,1), then the value of x is:

Simplify each side of the equation by converting the inverse trigonometric functions into standard trigonometric ratios.

● Video Walkthrough
Step 1: Simplify the Left Hand Side (LHS)✦ Active

Let θ=tan−1⁡(x2). Then tan⁡θ=x2. Construct a right triangle with opposite side x2 and adjacent side 1. The hypotenuse is (x2)2+12=2x2+1.

sin⁡(tan−1⁡(x2))=sin⁡θ=x22x2+1
Step 2: Simplify the Right Hand Side (RHS)○ Expand

Let ϕ=sin−1⁡1−x2. Then sin⁡ϕ=1−x2. Since x∈(0,1), ϕ∈(0,π2). Using the identity cos2⁡ϕ=1−sin2⁡ϕ, we get cos2⁡ϕ=1−(1−x2)=x2. Since ϕ is in the first quadrant, cos⁡ϕ=x.

cot⁡(sin−1⁡1−x2)=cot⁡ϕ=cos⁡ϕsin⁡ϕ=x1−x2
Step 3: Equate both sides and solve for x○ Expand

Equating the simplified LHS and RHS:

x22x2+1=x1−x2

Since x∈(0,1), x≠0, we can divide both sides by x:

22x2+1=11−x2

Square both sides:

22x2+1=11−x2 Cross-multiply: 2(1−x2)=2x2+1⟹2−2x2=2x2+1⟹1=4x2⟹x2=14. Since x∈(0,1), we take the positive root, so x=12.
💡 Teacher's Secret Hint

Always verify the solution against the given domain of x to ensure validity.

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