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CAT Nature of roots - Practice Questions & MCQ

Edited By admin | Updated on Oct 04, 2023 04:20 PM | #CAT

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If a+b\neq 2c   and  a,b,c\; \epsilon \; Q  then the number of rational roots of equation\left ( a+b-2c \right )x^{2}+\left ( b+c-2a \right )x+\left ( c+a-2b \right )= 0  equals:

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Nature of roots

Study Notes: Nature of Roots

Introduction to Quadratic Equations

  • A quadratic equation is an equation of the form \mathrm{ax^2 + bx + c = 0,} where a, b, and c are coefficients.
  • Quadratic equations have a degree of 2, indicating that the highest power of the variable is 2.
  • The solutions of a quadratic equation are called roots.
  • Quadratic equations can have zero, one, or two distinct real roots, based on the discriminant.

Discriminant

  • The discriminant of a quadratic equation is defined as \mathrm{b^2 - 4ac.}
  • The value of the discriminant determines the nature of the roots.
  • If the discriminant is positive, the quadratic equation has two distinct real roots.
  • If the discriminant is zero, the quadratic equation has one real root.
  • If the discriminant is negative, the quadratic equation has two complex conjugate roots.

Type of Roots

  • Real and Different Roots: If the discriminant is positive, the roots are real and different.
  • Real and Equal Roots: If the discriminant is zero, the roots are real and equal.
  • Complex Roots: If the discriminant is negative, the roots are complex conjugates, i.e. in the form of a + bi.

Examples of Nature of Roots

Example 1:

  • Solve the equation \mathrm{2x^2 + 5x + 2 = 0} and determine the nature of its roots.
  • Using the quadratic formula, \mathrm{x = (-b \pm \sqrt(b^2 - 4ac))/(2a),}
  • Here, \mathrm{a = 2, b = 5, and c = 2.}
  • Calculating the discriminant: \mathrm{b^2 - 4ac = 5^2 - 4(2)(2) = 25 - 16 = 9.}
  • As the discriminant is positive \mathrm{(9 > 0),} the equation has two distinct real roots.

Example 2:

  • Solve the equation \mathrm{3x^2 - 6x + 3 = 0} and determine the nature of its roots.
  • Using the quadratic formula,\mathrm{ x = (-b \pm \sqrt(b^2 - 4ac))/(2a),}
  • Here, a = 3, b = -6, and c = 3.
  • Calculating the discriminant: \mathrm{b^2 - 4ac = (-6)^2 - 4(3)(3) = 36 - 36 = 0.}
  • As the discriminant is zero (0 = 0), the equation has one real root.

Example 3:

  • Solve the equation \mathrm{x^2 + 4 = 0} and determine the nature of its roots.
  • Using the quadratic formula, \mathrm{x = (-b \pm \sqrt(b^2 - 4ac))/(2a),}
  • Here, \mathrm{a = 1, b = 0, and\: c = 4.}
  • Calculating the discriminant: \mathrm{b^2 - 4ac = 0 - 4(1)(4) = -16.}
  • As the discriminant is negative \mathrm{(-16 < 0),} the equation has two complex conjugate roots.

Tips and Tricks for Nature of Roots

  • Remember that the discriminant is the key to determine the nature of roots.
  • For quick mental calculation, if the discriminant is a perfect square, the roots are rational.
  • If the discriminant is a non-perfect square, the roots are irrational.
  • When solving multiple-choice questions, plugging the solution options into the equation can help determine the nature of roots.
  • Practice solving previous year's questions to gain familiarity with different scenarios and types of root nature.

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