JEE Main · Mathematics ↓ Falling

Limits, Continuity and Differentiability appeared 52 times across 3 years — 6% of Mathematics. This question is from Number of Real Solutions of Equations.

Year 2026 2025 2024 Total
Questions 12 24 16 52

The number of real solution(s) of the equation x²+3x+2= |x-3|, |x+2| is:

Solution & Explanation

Related Formula

The function f(x), g(x) chooses the lower vertical path between the two curves at any coordinate x.

Core Logic

Analyze the conditions for the right-hand function |x-3|, |x+2|:

  • The intersection of |x-3| = |x+2| happens at x - 3 = -(x + 2) ⇒ 2x = 1 ⇒ x = 0.5.
  • For x ≤ 0.5, |x+2| ≤ |x-3| ⇒ = |x+2|.
  • For x > 0.5, |x-3| ≤ |x+2| ⇒ = |x-3|.
  • Min function intersection graph for Q68 - JEE Main 2025 Evening
    Min function intersection graph for Q68 - JEE Main 2025 Evening

Step 1: Check Interval x ≤ -2

Here, |x+2| = -(x+2) = -x-2:

x² + 3x + 2 = -x - 2 ⇒ x² + 4x + 4 = 0 (x+2)² = 0 ⇒ x = -2

This is a valid solution as it lies precisely within the interval condition boundary.

Step 2: Check Interval -2 < x ≤ 0.5

Here, |x+2| = x+2:

x² + 3x + 2 = x + 2 ⇒ x² + 2x = 0 x(x+2) = 0 ⇒ x = 0 or x = -2

Only x = 0 fits inside this interval.

Step 3: Check Interval x > 0.5

Here, = |x-3| = 3-x:

x² + 3x + 2 = 3 - x ⇒ x² + 4x - 1 = 0 x = -4 ± √(16 - 4(1)(-1))2 = -2 ± √(5)

Evaluating values: -2 + √(5) ≈ 0.236, which does not satisfy x > 0.5. Thus, no real roots occur in this span.

Combining valid points, we find exactly 2 distinct real solutions (x = -2, 0).

Pattern Recognition

Sketching a rough visualization showing the parabola crossing below the sharp wedge of the combined absolute values makes it visually clear that there are exactly two crossing points, confirming the algebraic count.

Chapter Mix

Class 11 Mathematics: Quadratic Equations Class 12 Mathematics: Limits, Continuity and Differentiability

Reference Study Guides

More Limits, Continuity and Differentiability Previous-Year Questions

Q10 jee_main_2026_21_jan_morning 1^infinity Limit Form with L'Hopital's Rule
Let f: R → (0, ∞) be a twice differentiable function such that f(3) = 18 , f'(3) = 0 and f''(3) = 4 . Then x → 1 ( ₑ ( (f(2 + x))/(f(3)) )(18)/((x-1)²) ) is equal to:
  • A. 1
  • B. 9
  • C. 2
  • D. 18

Solution

Related Formula

For a limit of 1∞ form, x → a [g(x)]h(x) equals:

e^ x → a h(x)[g(x) - 1]
Core Logic

Let T = x → 1 ( (f(x + 2))/(f(3)) )(18)/((x - 1)²). As x → 1, (f(x+2))/(f(3)) → (f(3))/(f(3)) = 1. The exponent goes to ∞. This is a standard 1∞ form.

T = e^ x → 1 (18)/((x - 1)²) ( (f(x + 2) - f(3))/(f(3)) )
Step 1: Simplify Exponent Limit

Given f(3) = 18:

T = e^ x → 1 (18)/((x - 1)²) ( (f(x + 2) - f(3))/(18) ) T = e^ x → 1 (f(x + 2) - f(3))/((x - 1)²)

This is a (0)/(0) form limit.

Step 2: Apply L'Hopital's Rule

Differentiate numerator and denominator w.r.t x:

T = e^ x → 1 (f'(x + 2))/(2(x - 1))

This is still a (0)/(0) form since f'(3) = 0. Apply L'Hopital's Rule again:

T = e^ x → 1 (f''(x + 2))/(2)

Substitute x = 1:

T = e(f''(3))/(2)
Step 3: Final Calculation

Given f''(3) = 4:

T = e(4)/(2) = e²

The question asks for ₑ(T):

ₑ(T) = ₑ(e²) = 2
Pattern Recognition

When expanding f(x) around an extrema (f'(a)=0) inside a 1∞ limit form, double L'Hopital isolates the second derivative divided by the Taylor factorial (2! = 2). The limit elegantly shrinks directly to f''(a)/2.

Chapter Mix

Class 11 Maths: Limits and Derivatives Class 12 Maths: Limits, Continuity and Differentiability

Q3 jee_main_2026_21_jan_evening Differentiation
Let f(x) = x³ + x² f'(1) + 2x f''(2) + f'''(3), x in R. Then the value of f'(5) is :
  • A. (62)/(5)
  • B. (657)/(5)
  • C. (2)/(5)
  • D. (117)/(5)

Solution

Related Formula
(d)/(dx) (xⁿ) = nxⁿ⁻¹
Core Logic

Differentiate the given polynomial function iteratively to find expressions for f'(x) and f''(x), treating f'(1), f''(2), and f'''(3) as constant values.

Step 1: First and Second Derivatives
f'(x) = 3x² + 2x f'(1) + 2f''(2) f''(x) = 6x + 2f'(1)

Substitute x = 2 into the second derivative to create a relation:

f''(2) = 12 + 2f'(1)
Step 2: Substitute and Solve for Constants

Substitute f''(2) back into f'(x):

f'(x) = 3x² + 2x f'(1) + 2(12 + 2f'(1)) f'(x) = 3x² + 2(x + 2)f'(1) + 24

Now put x = 1 to solve for f'(1):

f'(1) = 3(1)² + 2(1 + 2)f'(1) + 24 f'(1) = 3 + 6f'(1) + 24 -5f'(1) = 27 f'(1) = -(27)/(5)
Step 3: Calculate Required Value

Determine the exact form of f'(x):

f'(x) = 3x² + 2(x + 2)(-(27)/(5)) + 24 f'(x) = 3x² - (54)/(5)x - (108)/(5) + (120)/(5) f'(x) = 3x² - (54)/(5)x + (12)/(5)

Substitute x = 5 to find f'(5):

f'(5) = 3(25) - (54)/(5)(5) + (12)/(5) f'(5) = 75 - 54 + (12)/(5) = 21 + (12)/(5) = (105 + 12)/(5) = (117)/(5)
Pattern Recognition

Treat derivatives evaluated at specific points (like f'(1)) as fixed scalar constants. Substitute values back sequentially to solve the linear system of constants.

Chapter Mix

Class 12 Maths: Method of Differentiation

Q21 jee_main_2026_21_jan_evening Limits of Sum
Let [·] denote the greatest integer function and f(x)= n→∞ 1n³Σk=1ⁿ[ k²3x]. Then 12Σj=1∞f(j) is equal to
Numerical Answer. Answer: 2 to 2

Solution

Related Formula
Sandwich Theorem for greatest integer function: x - 1 < [x] ≤ x Σk=1ⁿ k² = (n(n+1)(2n+1))/(6)
Core Logic

Evaluate f(x) using Squeeze Theorem on the summation bounds due to the Greatest Integer Function.

(k²)/(3^x) - 1 < [(k²)/(3^x)] ≤ (k²)/(3^x)
Step 1: Evaluate Limit f(x)

Sum over bounds:

Σk=1ⁿ ( (k²)/(3^x) - 1 ) < Σk=1ⁿ [ (k²)/(3^x) ] ≤ Σk=1ⁿ (k²)/(3^x) (1)/(3^x) (n(n+1)(2n+1))/(6) - n < Σk=1ⁿ [ (k²)/(3^x) ] ≤ (1)/(3^x) (n(n+1)(2n+1))/(6)

Divide by n³ and apply limit n → ∞:

n → ∞ ( (2n³ + 3n² + n)/(6n³ · 3^x) - (1)/(n²) ) < f(x) ≤ n → ∞ (2n³ + 3n² + n)/(6n³ · 3^x) f(x) = (2)/(6 · 3^x) = (1)/(3 · 3^x) = 13x+1
Step 2: Evaluate Final Summation

We need 12Σj=1∞ f(j):

12 Σj=1∞ 13j+1 = 12 ( (1)/(3²) + (1)/(3³) + … )

This is an infinite geometric progression with a = (1)/(9) and r = (1)/(3).

Sum = (a)/(1 - r) = (1/9)/(1 - 1/3) = (1/9)/(2/3) = (1)/(6)

Finally, 12 × (1)/(6) = 2.

Pattern Recognition

When evaluating infinite limits over greatest integer sums n → ∞ 1np+1 Σ [k^p/C], the G.I.F brackets can be safely replaced by exact values due to Sandwich theorem bounding the -1 residual to 0.

Chapter Mix

Class 11 Maths: Limits, Continuity and Differentiability Class 11 Maths: Sequence and Series

Q5 jee_main_2026_22_january_evening Limits using Expansion
If x → 0 e(a-1)x + 2 bx + (c-2)e-xx x - ₑ(1+x) = 2, then a² + b² + c² is equal to:
  • A. 5
  • B. 3
  • C. 7
  • D. 9

Solution

Related Formula

Standard Taylor series expansions:

e^x = 1 + x + (x²)/(2!) + , x = 1 - (x²)/(2!) + , ₑ(1+x) = x - (x²)/(2) +
Core Logic

Expand numerator and denominator around x = 0: Denominator: x(1 - (x²)/(2)) - (x - (x²)/(2)) = (x²)/(2) + O(x³). For limit to be finite, coefficients of x⁰ and x¹ in numerator must be zero:

  • Coefficient of x⁰: 1 + 2 + c - 2 = 0 c = -1
  • Coefficient of x¹: (a-1) - (c-2) = 0 a - 1 + 3 = 0 a = -2
Step 1: Coefficient of x^2

Numerator coefficient of x² is ((a-1)²)/(2) - b² + (c-2)/(2). Given limit value is 2:

(((a-1)²)/(2) - b² + (c-2)/(2))/(1/2) = 2 (9)/(2) - b² - (3)/(2) = 1 b² = 2
Step 2: Final Calculation
a² + b² + c² = (-2)² + 2 + (-1)² = 4 + 2 + 1 = 7
Pattern Recognition

Match powers of x in Taylor series to resolve indeterminate limit form (0)/(0).

Chapter Mix

Class 11 Maths: Limits, Continuity and Differentiability

Q15 jee_main_2026_22_january_evening Points of Discontinuity and Min Function
Let [·] denote the greatest integer function, and let f(x) = √(2)x, x². Let S = x in (-2,2) : the function g(x) = |x|[x²] is discontinuous at x. Then Σx in S f(x) equals:
  • A. 2 - √(2)
  • B. 2√(6) - 3√(2)
  • C. 1 - √(2)
  • D. √(6) - 2√(2)

Solution

Related Formula

Greatest integer function [x²] is discontinuous where x² takes integer values, except possibly where |x| = 0.

Core Logic

In (-2, 2), x² in [0, 4). Integer values occur at x = 0, ± 1, ±√(2), ±√(3). At x = 0, g(0) = 0 and x → 0 g(x) = 0, so g(x) is continuous at x = 0. Points of discontinuity: S = -1, 1, -√(2), √(2), -√(3), √(3).

Step 1: Evaluate f(x) for x in S

For f(x) = √(2)x, x²:

  • f(-1) = -√(2), 1 = -√(2)
  • f(1) = √(2), 1 = 1
  • f(-√(2)) = -2, 2 = -2
  • f(√(2)) = 2, 2 = 2
  • f(-√(3)) = -√(6), 3 = -√(6)
  • f(√(3)) = √(6), 3 = √(6)
Step 2: Summation
Σx in S f(x) = -√(2) + 1 - 2 + 2 - √(6) + √(6) = 1 - √(2)
Pattern Recognition

Check origin continuity explicitly for |x|[x²]; evaluate √(2)x, x² case-by-case on set S.

Chapter Mix

Class 12 Maths: Limits, Continuity and Differentiability

More Limits, Continuity and Differentiability Questions — jee_main_2025_24_jan_evening

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