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Trigonometric Functions appeared 27 times across 3 years — 3.1% of Mathematics. This question is from Trigonometric Identities.

Year 2026 2025 2024 Total
Questions 10 10 7 27

If x + ² x = 1, x in (0, (π)/(2)), then ( ¹² x + ¹² x) + 3 ( ¹⁰ x + ¹⁰ x + ⁸ x + ⁸ x) + ( ⁶ x + ⁶ x) is equal to

Solution & Explanation

Related Formula

Fundamental identities:

² x + ² x = 1 x = ( x)/( x)

Algebraic identity for a perfect cube:

(A + B)³ = A³ + 3A²B + 3AB² + B³
Core Logic

Given equation:

x + ² x = 1 x = 1 - ² x = ² x

Dividing both sides by ² x:

( x)/( ² x) = 1 x x = 1 x = x
Step 1: Simplify the Expression

Since x = x, we can substitute x with x throughout the given expression:

( ¹² x + ¹² x) + 3( ¹⁰ x + ¹⁰ x + ⁸ x + ⁸ x) + ( ⁶ x + ⁶ x) = 2 ¹² x + 6 ¹⁰ x + 6 ⁸ x + 2 ⁶ x = 2[ ¹² x + 3 ¹⁰ x + 3 ⁸ x + ⁶ x]
Step 2: Apply the Cubic Identity

Notice that the expression inside the brackets matches the expansion of a perfect cube:

= 2[( ⁴ x + ² x)³]

Since ² x = x, it follows that ⁴ x = ² x. Substituting these back in:

= 2[( ² x + x)³]

We know from the problem statement that x + ² x = 1. Therefore:

= 2(1)³ = 2

Pattern Recognition

When given x + ² x = 1, the substitution ² x = x or x = x is a classic identity trick. Recognizing binomial coefficients (1, 3, 3, 1) immediately signals to condense into a full cube structure.

Chapter Mix

Class 11 Mathematics: Trigonometric Functions

Reference Study Guides

More Trigonometric Functions Previous-Year Questions — Page 6

Q19 jee_main_2024_30_jan_morning Trigonometric Equations
If 2 ³ x + 2x x + 4 x - 4 = 0 has exactly 3 solutions in the interval [0,(nπ)/(2)], nin N, then the roots of the equation x² + nx + (n - 3) = 0 belong to :
  • A. (0,∞)
  • B. (-∞,0)
  • C. (- √(17)2, √(17)2)
  • D. Z

Solution

Related Formula
2x = 2 x x
Core Logic

Given equation: 2 ³ x + 2x x + 4 x - 4 = 0 Expand 2x:

2 ³ x + 2 x ² x + 4 x - 4 = 0

Factor out 2 x from the first two terms:

2 x ( ² x + ² x) + 4 x - 4 = 0

Since ² x + ² x = 1:

2 x (1) + 4 x - 4 = 0 6 x - 4 = 0 ⇒ x = (4)/(6) = (2)/(3)
Step 1: Finding appropriate interval for exactly 3 roots

We need exactly 3 solutions in [0, (nπ)/(2)]. The line y = 2/3 intersects the sine wave y = x twice in every 2π interval. In [0, π], there are 2 solutions. In [π, 2π], there are 0 solutions. In [2π, 3π], there are 2 solutions (total 4 solutions). To get exactly 3 solutions, the interval must stretch past the first root in [2π, 3π], but not reach the second root in that interval. However, the interval is defined as (nπ)/(2). Let's check endpoints (nπ)/(2): For n=4: [0, 2π] has 2 solutions. For n=5: [0, (5π)/(2)] includes [2π, 2π + (π)/(2)]. Since x = 2/3 happens in (0, π/2), there is exactly 1 solution in [2π, 5π/2]. Thus, total solutions = 3 for n=5.

Step 2: Solving quadratic equation

Given n = 5, the quadratic equation is:

x² + 5x + 2 = 0

Using quadratic formula:

x = -5 ± √(25 - 8)2 = -5 ± √(17)2

The roots are approximately (-5 ± 4.12)/(2), which evaluates to roughly -0.44 and -4.56. Both roots are strictly negative.

Step 3: Determining interval membership

Since both roots are negative, they belong to the interval (-∞, 0).

Pattern Recognition

Collapsing complex trigonometric expressions often yields c₁ x = c₂. Overlaying horizontal line intersections on the sine graph bounds n rapidly by counting nodes.

Chapter Mix

Class 11 Maths: Trigonometric Functions Class 11 Maths: Complex Numbers and Quadratic Equations

Q15 jee_main_2024_31_jan_evening Trigonometric Equations
The number of solutions, of the equation ex - 2e- x = 2 is
  • A. 2
  • B. more than 2
  • C. 1
  • D. 0

Solution

Core Logic

Let ex = t, where t > 0 because exponential functions are strictly positive. Substitute into the equation:

t - (2)/(t) = 2 t² - 2t - 2 = 0

Solve for t using the quadratic formula:

t = 2 ± √(4 - 4(1)(-2))2 = 1 ± √(3)

Since t > 0, we discard 1 - √(3). Thus, t = 1 + √(3) ≈ 2.732. Now, equate back:

ex = 1 + √(3) x = ln(1 + √(3))

We know e ≈ 2.718. Since 1 + √(3) > e, it follows that ln(1 + √(3)) > 1. But the range of x is [-1, 1]. Therefore, x cannot equal a value strictly greater than 1. No real solution exists.

Chapter Mix

Class 11 Maths: Trigonometric Functions Class 12 Maths: Continuity and Differentiability

More Trigonometric Functions Questions — jee_main_2025_29_jan_evening

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