JEE Main · Mathematics → Steady

Trigonometric Functions appeared 43 times across 3 years — 5% of Mathematics. This question is from Trigonometric Equations.

Year 2026 2025 2024 Total
Questions 15 18 10 43

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 :

Solution & Explanation

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

Reference Study Guides

More Trigonometric Functions Previous-Year Questions — Page 9

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

Q16 jee_main_2024_31_jan_evening Properties of ITFs
If a = ⁻¹( (5)) and b = ⁻¹( (5)), then a² + b² is equal to
  • A. 4π² + 25
  • B. 8π² - 40π + 50
  • C. 4π² - 20π + 50
  • D. 25

Solution

Related Formula
⁻¹( x) = x - 2π for x in [3π/2, 5π/2] ⁻¹( x) = 2π - x for x in [π, 2π]
Core Logic

Evaluate a = ⁻¹( 5): The principal branch of ⁻¹ x is [-π/2, π/2]. 5 radians is approximately 5 × 57.3^° ≈ 286.5^° (in 4th quadrant). The equivalent angle in the principal domain is 5 - 2π. Thus, a = 5 - 2π.

Evaluate b = ⁻¹( 5): The principal branch of ⁻¹ x is [0, π]. 5 radians is in [π, 2π]. The equivalent angle is 2π - 5. Thus, b = 2π - 5.

Calculate a² + b²:

a² + b² = (5 - 2π)² + (2π - 5)²

= 2(5 - 2π)²

= 2(25 + 4π² - 20π) = 8π² - 40π + 50
Chapter Mix

Class 12 Maths: Inverse Trigonometric Functions

Q15 jee_main_2024_31_jan_morning Properties of Inverse Trigonometric Functions
For α, β, γ ≠ 0. If ⁻¹α + ⁻¹β + ⁻¹γ = π and (α + β + γ)(α - γ + β) = 3 αβ then γ equal to
  • A. √(3)2
  • B. 1√(2)
  • C. √(3) - 12√(2)
  • D. √(3)

Solution

Core Logic

Let ⁻¹α = A, ⁻¹β = B, ⁻¹γ = C. Given A + B + C = π. Since A = α, B = β, C = γ, α, β, γ act like the side lengths of a triangle divided by 2R by Sine rule. However, directly dealing with the relation:

(α + β + γ)(α + β - γ) = 3αβ
Step 1: Simplify Algebraic Relation
(α + β)² - γ² = 3αβ α² + β² + 2αβ - γ² = 3αβ α² + β² - γ² = αβ
Step 2: Triangle Identification

Divide by 2αβ:

(α² + β² - γ²)/(2αβ) = (1)/(2)

By Cosine Rule, C = (1)/(2). Since C = ⁻¹γ, we know C = γ. C = √(1 - γ²) = (1)/(2).

Step 3: Final Solution
1 - γ² = (1)/(4) γ² = (3)/(4)

Since C is an angle of a triangle (or sum equals π and elements are positive limits), γ = C > 0.

γ = √(3)2
Pattern Recognition

The expression (α + β + γ)(α + β - γ) = 3αβ perfectly mirrors the Cosine Rule standard form giving C = 1/2.

Chapter Mix

Class 12 Maths: Inverse Trigonometric Functions Class 11 Maths: Trigonometric Functions

More Trigonometric Functions Questions — jee_main_2024_30_jan_morning

Practice all Trigonometric Functions previous-year questions →

Rankbit System
JEE Physics: Waves (+15.5%) | Electrostatics: Concentric Shells (-29.7%) | Modern Physics: Photoelectric Clones (+34.2%) | Mathematics: Definite Integrals (+18.1%) | Chemistry: Coordination Splitting (-11.4%) | JEE Physics: Waves (+15.5%) | Electrostatics: Concentric Shells (-29.7%) | Modern Physics: Photoelectric Clones (+34.2%) | Mathematics: Definite Integrals (+18.1%) | Chemistry: Coordination Splitting (-11.4%)