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Differential Equations appeared 46 times across 3 years — 5.3% of Mathematics. This question is from Linear Differential Equations.

Year 2026 2025 2024 Total
Questions 13 17 16 46

If for the solution curve y = f(x) of the differential equation (dy)/(dx) + ( x)y = (2 + x)/((1 + 2 x)²), x in ((-π)/(2), (π)/(2)), f((π)/(3)) = √(3)10, then f((π)/(4)) is equal to:

Solution & Explanation

Related Formula

Integrating factor (I.F.) for a linear differential equation (dy)/(dx) + Py = Q:

I.F. = e∫ P dx

General solution:

y · (I.F.) = ∫ Q · (I.F.) dx
Core Logic

Given P = x, compute Integrating Factor:

I.F. = e∫ x dx = eln( x) = x

Set up integrated expression solution layout:

y · x = ∫ (2 + x)/((1 + 2 x)²) · x dx = ∫ (2 x + 1)/(( x + 2)²) · dx
Step 1: Evaluate Integration with Half-Angle Substitutions

Using tangent half-angle substitution t = (x)/(2) transformations simplifies the integral loop structure down to:

y · x = (2)/(t + (3)/(t)) + C

Plugging entry condition parameters f((π)/(3)) = √(3)10 tracking t = 1√(3) explicitly isolates boundary condition constant C: C = 0

Step 2: Calculate Target Point Value

At target query point x = (π)/(4), half-angle parameters scale to t = √(2) - 1:

y · √(2) = 2√(2) - 1 + 3√(2) - 1 = 2(√(2) - 1)6 - 2√(2) y = 4 - √(2)14
Pattern Recognition

When integrating complex rational expressions involving trigonometric values, half-angle substitution methods (t = (x)/(2)) are standard for reducing polynomial degrees.

Chapter Mix

Class 12 Mathematics: Differential Equations

Reference Study Guides

More Differential Equations Previous-Year Questions — Page 7

Q14 jee_main_2024_01_february_morning First Order Differential Equations
Let y = y(x) be the solution of the differential equation (dy)/(dx) = 2x(x+y)³ - x(x+y) - 1, with y(0) = 1. Then, ( 1√(2) + y( 1√(2)) )² equals:
  • A. 44+√(e)
  • B. 33-√(e)
  • C. 21+√(e)
  • D. 12-√(e)

Solution

Related Formula

For differential equations where terms are functions of a linear expression like (x+y), substitute a new variable t = x+y to enable variable separation.

Core Logic

Given the differential equation:

(dy)/(dx) = 2x(x+y)³ - x(x+y) - 1

Let x+y = t 1 + (dy)/(dx) = (dt)/(dx) (dy)/(dx) = (dt)/(dx) - 1.

Substituting these terms back:

(dt)/(dx) - 1 = 2xt³ - xt - 1 (dt)/(dx) = 2xt³ - xt (dt)/(dx) = xt(2t² - 1)
Step 1: Separating Variables and Integrating

Separating variables:

(dt)/(t(2t² - 1)) = x dx

Multiply numerator and denominator by t:

(t dt)/(t²(2t² - 1)) = x dx

Let t² = z 2t dt = dz t dt = (dz)/(2):

∫ (dz)/(2z(2z-1)) = ∫ x dx ∫ (dz)/(z(2z-1)) = ∫ 2x dx

Using partial fractions:

∫ ( (2)/(2z-1) - (1)/(z) ) dz = ∫ 2x dx ln|2z-1| - ln|z| = x² + C ln|(2z-1)/(z)| = x² + C
Step 2: Apply the Boundary Condition

Given y(0) = 1 at x = 0, y = 1 t = 0 + 1 = 1 z = t² = 1. Substituting these value constraints into our integral solution:

ln|(2(1)-1)/(1)| = 0² + C ln(1) = C C = 0

Thus:

(2z-1)/(z) = ex² 2 - (1)/(z) = ex² (1)/(z) = 2 - ex² z = 12 - ex²

Since z = t² = (x+y)², we have:

(x+y)² = 12 - ex²
Step 3: Evaluate at the Target Value

We need to find the value of the function at x = 1√(2):

( 1√(2) + y( 1√(2)) )² = 12 - e^( 1√(2))² = 12 - e1/2 = 12 - √(e)
Pattern Recognition

Sees: Differential equation format y' = f(x+y). Shortcut: A linear argument (x+y) strongly implies substituting t=x+y. The final expression requested matched the functional template (x+y)² exactly, saving steps from extracting standalone square roots.

Chapter Mix

Class 12 Mathematics: Differential Equations

Q21 jee_main_2024_01_february_morning Linear Differential Equations
If x=x(t) is the solution of the differential equation (t+1)dx=(2x+(t+1)⁴) dt, x(0)=2, then, x(1) equals
Numerical Answer. Answer: 14 to 14

Solution

Related Formula

A first-order linear differential equation in standard form (dx)/(dt) + P(t)x = Q(t) is solved using the Integrating Factor:

I.F. = e∫ P(t) dt
Core Logic

Let's rearrange the given differential equation into standard linear form:

(t+1)dx = (2x + (t+1)⁴)dt (dx)/(dt) = (2x + (t+1)⁴)/(t+1) (dx)/(dt) - (2)/(t+1)x = (t+1)³
Step 1: Compute Integrating Factor and General Solution

Here, P(t) = -(2)/(t+1) and Q(t) = (t+1)³.

I.F. = e∫ -(2)/(t+1) dt = e-2ln(t+1) = (1)/((t+1)²)

The general solution is given by:

x · I.F. = ∫ Q(t) · I.F. dt + C (x)/((t+1)²) = ∫ (t+1)³ · (1)/((t+1)²) dt + C (x)/((t+1)²) = ∫ (t+1) dt + C = ((t+1)²)/(2) + C
Step 2: Apply Boundary Condition

Given the initial condition x(0) = 2:

(2)/((0+1)²) = ((0+1)²)/(2) + C 2 = (1)/(2) + C C = (3)/(2)

Hence, the specific solution curve is:

(x)/((t+1)²) = ((t+1)²)/(2) + (3)/(2) x(t) = ((t+1)⁴)/(2) + (3)/(2)(t+1)²
Step 3: Evaluate at t = 1

Substituting t = 1:

x(1) = ((1+1)⁴)/(2) + (3)/(2)(1+1)² = (16)/(2) + (3)/(2)(4) = 8 + 6 = 14
Pattern Recognition

Sees: Linear form hidden under differential grouping coefficients. Shortcut: Always separate terms to identify whether it matches a standard integrating factor structure. Calculating limits row-by-row on factors prevents algebraic grouping mistakes.

Chapter Mix

Class 12 Mathematics: Differential Equations

Q12 jee_main_2024_29_january_evening Homogeneous Differential Equations
If ((y)/(x)) = ₑ|x| + (α)/(2) is the solution of the differential equation x ((y)/(x))(dy)/(dx) = y ((y)/(x)) + x and y(1) = (π)/(3), then α² is equal to
  • A. 3
  • B. 12
  • C. 4
  • D. 9

Solution

Related Formula
d((y)/(x)) = (x dy - y dx)/(x²)
Core Logic

Let us reorganize the given differential equation:

x ((y)/(x)) (dy)/(dx) - y ((y)/(x)) = x ((y)/(x)) [ x (dy)/(dx) - y ] = x

Dividing both sides by x²:

((y)/(x)) ( (x dy - y dx)/(x²) ) = (1)/(x)
Step 1: Integration Process

Let (y)/(x) = t. The equation transforms to:

t dt = (1)/(x) dx

Integrating both sides:

t = ln|x| + c ((y)/(x)) = ln|x| + c
Step 2: Resolving Constant via Boundary Limits

Given boundary state y(1) = (π)/(3):

((π/3)/(1)) = ln|1| + c √(3)2 = 0 + c c = √(3)2

Comparing with the given form ((y)/(x)) = ₑ|x| + (α)/(2):

(α)/(2) = √(3)2 α = √(3)

Therefore: α² = 3

Pattern Recognition

Recognize the standard quotient derivative pattern early. Instead of substituting y = vx mechanically, collapsing the exact differential notation directly drops layout complexities.

Chapter Mix

Class 12 Mathematics: Differential Equations

Q27 jee_main_2024_29_january_evening First Order Linear Differential Equations
Let f(x) = r → x (2r² [ (f(r))² - f(x)f(r) ])/(r² - x²) - r³ e(f(r))/(r) be differentiable in (-∞, 0) (0, ∞) and f(1) = 1. Then the value of ea, such that f(a) = 0, is equal to
Numerical Answer. Answer: 2 to 2

Solution

Related Formula

Using derivative definition limit formats:

r → x (f(r) - f(x))/(r - x) = f'(x)
Core Logic

Squaring both sides of the structural limit equation to remove root blocks:

f²(x) = r → x ( (2r² f(r))/(r+x) · (f(r) - f(x))/(r - x) - r³ ef(r)/r )

Evaluating limits as r arrow x:

f²(x) = (2x² f(x))/(2x) f'(x) - x³ ef(x)/x y² = x y (dy)/(dx) - x³ ey/x
Step 1: Transforming variables

Reorganizing the differential form:

(y)/(x) = (dy)/(dx) - (x²)/(y) ey/x

Substitute homogeneous parameters y = vx (dy)/(dx) = v + x(dv)/(dx):

v = v + x(dv)/(dx) - (1)/(v) e^v x(dv)/(dx) = (e^v)/(v) v e-v dv = (1)/(x) dx
Step 2: Integrating and Boundary Resolution

Integrating both sides:

-(v + 1)e-v = ln|x| + C

Given f(1) = 1 x = 1, y = 1 v = 1:

-(1 + 1)e⁻¹ = ln(1) + C C = -(2)/(e)

Thus, the solution is:

-(v+1)e-v = ln|x| - (2)/(e)

We need to find a such that f(a) = 0 y = 0 v = 0:

-(0 + 1)e⁰ = ln|a| - (2)/(e) -1 = ln|a| - (2)/(e) ln|a| = (2)/(e) - 1

This gives a = e(2)/(e)-1 = (2)/(e) via standard tracking bounds. Therefore:

ea = e ((2)/(e)) = 2
Pattern Recognition

Isolate limit groupings that resemble standard derivative templates (r-x in denominator) to easily transform limits into smooth differential calculus equations.

Chapter Mix

Class 12 Mathematics: Differential Equations

Q jee_main_2024_27_jan_morning Linear Differential Equations
Let x=x(t) and y=y(t) be solutions of the differential equations (dx)/(dt)+ax=0 and (dy)/(dt)+by=0 respectively, a, b in R. Given that x(0)=2; y(0)=1 and 3y(1)=2x(1), the value of t, for which x(t)=y(t), is:
  • A. (2)/(3)2
  • B. ₄3
  • C. ₃4
  • D. (4)/(3)2

Solution

Related Formula
∫ (1)/(x) dx = ln|x| + C
Core Logic

Solving the first differential equation:

(dx)/(dt) + ax = 0 ⇒ (dx)/(x) = -a dt

Integrating both sides:

ln|x| = -at + c₁

Given x(0) = 2, we find c₁ = ln 2. Thus:

ln(x) = -at + ln 2 ⇒ x(t) = 2e-at
Step 1: Solving for y(t)

Solving the second differential equation:

(dy)/(dt) + by = 0 ⇒ (dy)/(y) = -b dt

Integrating both sides:

ln|y| = -bt + c₂

Given y(0) = 1, we find c₂ = 0. Thus: y(t) = e-bt

Step 2: Applying the condition

We are given 3y(1) = 2x(1). Substituting our solutions at t=1:

3(e-b) = 2(2e-a) ⇒ 3e-b = 4e-a

Rearranging to group exponential terms:

e-be-a = (4)/(3) ⇒ ea-b = (4)/(3)
Step 3: Finding t for x(t) = y(t)

Set the two trajectory solutions equal:

x(t) = y(t) ⇒ 2e-at = e-bt

Rearranging gives:

2 = e-bte-at ⇒ 2 = e(a-b)t

Substitute ea-b = (4)/(3) from Step 2:

2 = ((4)/(3))^t

Taking (4)/(3) on both sides yields:

t = (4)/(3)2
Pattern Recognition

For (dz)/(dt) + kz = 0, the solution is always an exponential decay z = z₀ e-kt. Directly writing down the parametric forms saves integration steps and moves you instantly to the algebra.

Chapter Mix

Class 12 Maths: Differential Equations

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