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Quadratic Equations appeared 26 times across 3 years — 3% of Mathematics. This question is from Newton's Theorem on Roots.

Year 2026 2025 2024 Total
Questions 11 10 5 26

Let α and β be the roots of x² + √(3)x - 16 = 0, and γ and δ be the roots of x² + 3x - 1 = 0. If Pₙ = αⁿ + βⁿ and Qₙ = γⁿ + δⁿ, then P₂₅ + √(3)P₂₄2P₂₃ + Q₂₅ - Q₂₃Q₂₄ is equal to ______

Solution & Explanation

Related Formula

Newton's Theorem for roots: If α, β satisfy ax² + bx + c = 0 and Sₙ = αⁿ + βⁿ, then:

aSₙ + bSₙ₋₁ + cSₙ₋₂ = 0
Core Logic

Apply Newton's Theorem directly to the first equation x² + √(3)x - 16 = 0:

Pₙ + √(3)Pₙ₋₁ - 16Pₙ₋₂ = 0

For n = 25:

P₂₅ + √(3)P₂₄ - 16P₂₃ = 0 P₂₅ + √(3)P₂₄ = 16P₂₃

Dividing both sides by 2P₂₃:

P₂₅ + √(3)P₂₄2P₂₃ = 16P₂₃2P₂₃ = 8
Step 1: Evaluation of the Second Part

For the second equation x² + 3x - 1 = 0:

Qₙ + 3Qₙ₋₁ - Qₙ₋₂ = 0 Qₙ - Qₙ₋₂ = -3Qₙ₋₁

For n = 25:

Q₂₅ - Q₂₃ = -3Q₂₄

Dividing both sides by Q₂₄:

Q₂₅ - Q₂₃Q₂₄ = -3
Step 2: Total Calculation

Add both evaluated components:

Total Expression Value = 8 + (-3) = 5
Pattern Recognition

Shortcut: High sequential indices (25, 24, 23) indicate recurrence via Newton's Theorem. Relate Pₙ and Qₙ directly to their characteristic quadratic polynomials to evaluate the ratios in one step without calculating powers.

Evaluation Rubric / Model Answer

Option (C)

Chapter Mix

Class 11 Mathematics: Quadratic Equations

More Quadratic Equations Previous-Year Questions — Page 5

Q59 jee_main_2025_29_jan_morning Equations Reducible to Quadratic Forms
The number of solutions of the equation ((9)/(x) - 9√(x) +2)((2)/(x) - 7√(x) +3) = 0 is:
  • A. 2
  • B. 4
  • C. 1
  • D. 3

Solution

Related Formula
Substitute variable to convert non-linear form: α = 1√(x) (x > 0)
Core Logic

Let 1√(x) = α. The equation reduces to a product of two quadratics:

(9α² - 9α + 2)(2α² - 7α + 3) = 0
Step 1: Factorize the components

First quadratic: 9α² - 9α + 2 = 0 (3α - 2)(3α - 1) = 0 α = (2)/(3), (1)/(3) Second quadratic: 2α² - 7α + 3 = 0 (2α - 1)(α - 3) = 0 α = (1)/(2), 3

Step 2: Solve for x

Since α = 1√(x) x = (1)/(α²). For α = (1)/(3) x = 9 For α = (1)/(2) x = 4 For α = (2)/(3) x = (9)/(4) For α = 3 x = (1)/(9) All 4 values are positive and valid.

Pattern Recognition

Always check constraints first (x > 0 due to √(x) in denominator). Since all roots α > 0, every single algebraic root maps to a real distinct solution.

Chapter Mix

Class 11 Mathematics: Quadratic Equations

Q9 jee_main_2024_01_february_morning Equations Reducible to Quadratic Form
Let S=xin R:(√(3)+√(2))x+(√(3)-√(2))x=10. Then the number of elements in S is:
  • A. 4
  • B. 0
  • C. 2
  • D. 1

Solution

Related Formula

Conjugate Surd Identity:

(√(a) + √(b))(√(a) - √(b)) = a - b
Core Logic

Observe the base components of the exponents:

(√(3) + √(2))(√(3) - √(2)) = 3 - 2 = 1

Therefore, we can express one base as the reciprocal of the other:

√(3) - √(2) = 1√(3) + √(2)

The equation becomes:

(√(3) + √(2))x + 1(√(3) + √(2))x = 10
Step 1: Formulate the Quadratic Equation

Let (√(3) + √(2))x = t. Then:

t + (1)/(t) = 10 t² - 10t + 1 = 0

Solving for t using the quadratic formula:

t = 10 ± (-10)² - 4(1)(1)2 = 10 ± √(96)2 = 5 ± 2√(6)
Step 2: Solve for x

Notice that (5 ± 2√(6)) can be written as square powers of the original base:

(√(3) ± √(2))² = 3 + 2 ± 2√(6) = 5 ± 2√(6)

Thus, we have:

  • For t = 5 + 2√(6) (√(3) + √(2))x = (√(3) + √(2))² x = 2
  • For t = 5 - 2√(6) (√(3) + √(2))x = (√(3) - √(2))² = (√(3) + √(2))⁻² x = -2
  • Therefore, the distinct real solutions are x = 2 and x = -2. The number of elements in set S is 2.

Pattern Recognition

Sees: Rational conjugate bases added with inverse matching variables. Shortcut: Whenever you see an equation of the form A^x + B^x = C where AB = 1, the solution will always be symmetric (± x₀). Checking x=2 explicitly gives (√(3)+√(2))² + (√(3)-√(2))² = (5+2√(6)) + (5-2√(6)) = 10, confirming ± 2 immediately.

Chapter Mix

Class 11 Mathematics: Quadratic Equations Class 9 Mathematics: Number Systems (Rationalization)

Q28 jee_main_2024_30_january_evening Modulus Equations
The number of real solutions of the equation x(x² + 3|x| + 5|x - 1| + 6|x - 2|) = 0 is
Numerical Answer. Answer: 1 to 1

Solution

Related Formula
Zero Product Property: A · B = 0 A = 0 or B = 0
Core Logic

Given equation:

x(x² + 3|x| + 5|x - 1| + 6|x - 2|) = 0

This factors into two possibilities:

  • x = 0
  • x² + 3|x| + 5|x - 1| + 6|x - 2| = 0
Step 1: Evaluating the Modulus Term

Look at the second factor: f(x) = x² + 3|x| + 5|x - 1| + 6|x - 2|. Notice that all terms inside are strictly non-negative:

  • x² ≥ 0
  • 3|x| ≥ 0
  • 5|x - 1| ≥ 0
  • 6|x - 2| ≥ 0
  • For the sum to be 0, every single term must be simultaneously zero. x² = 0 x = 0 However, if x = 0, then 5|x-1| = 5(1) = 5 ≠ 0. Therefore, there is no real value of x that makes this entire second factor equal to zero.

Step 2: Conclusion

The only valid solution to the equation is x = 0 from the first factor. Thus, there is exactly 1 real solution.

Pattern Recognition

A sum of absolute values and squares set to 0 requires all individual components to hit 0 concurrently. If they have different zero-nodes (0, 1, 2), the sum can never be 0.

Chapter Mix

Class 11 Maths: Quadratic Equations

Q22 jee_main_2024_31_jan_evening Roots of Quadratic Equation
Let a, b, c be the length of three sides of a triangle satisfying the condition (a² + b²)x² - 2b(a + c)x + (b² + c²) = 0. If the set of all possible values of x is the interval (α, β) then 12(α² + β²) is equal to
Numerical Answer. Answer: 36 to 36

Solution

Core Logic

Given equation: (a²+b²)x² - 2b(a+c)x + b²+c² = 0. Expand and rearrange into perfect squares:

(a²x² - 2abx + b²) + (b²x² - 2bcx + c²) = 0 (ax - b)² + (bx - c)² = 0

Since squares must be non-negative, each term is zero:

ax - b = 0 x = (b)/(a) bx - c = 0 x = (c)/(b)

Thus, b = ax and c = bx = ax². Since a,b,c form a triangle, the triangle inequality holds:

  • a + b > c a + ax > ax² x² - x - 1 < 0 1-√(5)2 < x < 1+√(5)2
  • a + c > b a + ax² > ax x² - x + 1 > 0 (Always true for real x)
  • b + c > a ax + ax² > a x² + x - 1 > 0 x > -1+√(5)2 or x < -1-√(5)2.
  • Taking the intersection (and noting x > 0 since sides are positive):

√(5)-12 < x < √(5)+12

So, α = √(5)-12 and β = √(5)+12. Calculate 12(α² + β²):

12 ( 6-2√(5)4 + 6+2√(5)4 ) = 12 ( (12)/(4) ) = 36
Chapter Mix

Class 11 Maths: Complex Numbers and Quadratic Equations Class 11 Maths: Straight Lines

Q1 jee_main_2024_31_jan_morning Nature of Roots
For 0 < c < b < a, let (a + b - 2c)x² + (b + c - 2a)x + (c + a - 2b) = 0 and α ≠ 1 be one of its root. Then, among the two statements (I) If α in (-1,0), then b cannot be the geometric mean of a and c (II) If α in (0,1), then b may be the geometric mean of a and c
  • A. Both (I) and (II) are true
  • B. Neither (I) nor (II) is true
  • C. Only (II) is true
  • D. Only (I) is true

Solution

Related Formula
Sum of coefficients = 0 x = 1 is a root.
Core Logic

Given f(x) = (a + b - 2c)x² + (b + c - 2a)x + (c + a - 2b) = 0. Substituting x = 1:

f(1) = a + b - 2c + b + c - 2a + c + a - 2b = 0

Thus, one root is 1. Let the other root be α.

Step 1: Find the other root

Product of roots = (c + a - 2b)/(a + b - 2c). Since one root is 1, we have:

α · 1 = (c + a - 2b)/(a + b - 2c) α = (c + a - 2b)/(a + b - 2c)
Step 2: Analyze Statement (I)

If -1 < α < 0:

-1 < (c + a - 2b)/(a + b - 2c) < 0

This implies b > (a + c)/(2) and b + c < 2a. Therefore, b cannot be the Geometric Mean of a and c. Statement (I) is true.

Step 3: Analyze Statement (II)

If 0 < α < 1:

0 < (c + a - 2b)/(a + b - 2c) < 1

This gives b > c and b < (a + c)/(2). Therefore, b may be the Geometric Mean between a and c. Statement (II) is true.

Pattern Recognition

When coefficients in a quadratic equation are cyclic and sum to 0, one root is always 1. The other root is directly c/a.

Chapter Mix

Class 11 Maths: Quadratic Equations Class 11 Maths: Sequences and Series

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