EquationsMCQMTP Jun 23 Series IQuestion 1094 of 221
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If one root of the quadratic equation is 2−3\displaystyle 2 - 3\displaystyle \sqrt{3} from the equation, except that the roots are irrational. Then find the Quadratic equation.

Select Your Answer (Keyboard: A, B, C, D)
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Correct Answer

✅ Option a — x2−4x+1=0\displaystyle x^2 - 4x + 1 = 0

All Options:

  • Ax2−4x+1=0\displaystyle x^2 - 4x + 1 = 0
  • Bx2+4x−1=0\displaystyle x^2 + 4x - 1 = 0
  • Cx2−4x−1=0\displaystyle x^2 - 4x - 1 = 0
  • Dx2+4x+1=0\displaystyle x^2 + 4x + 1 = 0

Detailed Solution & Explanation

If one root of a quadratic equation with rational coefficients is irrational, say α=2−3\displaystyle α=2−3\displaystyle \alpha = 2 - \sqrt{3}, then the other root β\displaystyle β\displaystyle \beta must be its irrational conjugate:
β=2+3β=2+3\displaystyle \beta = 2 + \sqrt{3}
Now, calculate the sum and product of the roots:
1. **Sum of roots (S\displaystyle S):**
S=α+β=(2−3)+(2+3)=4S = α+β\displaystyle \alpha + \beta = (2 - 3\displaystyle \sqrt{3}) + (2 + 3\displaystyle \sqrt{3}) = 4
2. **Product of roots (P\displaystyle P):**
P=αβ=(2−3)(2+3)=(2)2−(3)2=4−3=1P = α\displaystyle \alphaβ\displaystyle \beta = (2 - 3\displaystyle \sqrt{3})(2 + 3\displaystyle \sqrt{3}) = (2)^2 - (3\displaystyle \sqrt{3})^2 = 4 - 3 = 1
The general form of a quadratic equation is:
x2−Sx+P=0x^2 - Sx + P = 0
Substitute the sum (S=4\displaystyle S = 4) and product (P=1\displaystyle P = 1):
x2−4x+1=0x^2 - 4x + 1 = 0
This corresponds to Option a.

**Option a**

About This Chapter: Equations

Paper

Paper 3: Quantitative Aptitude

Weightage

4-6 Marks

Key Topics

Linear, Quadratic and Cubic Equations

This chapter covers Linear, Quadratic and Cubic Equations and is part of Paper 3: Quantitative Aptitude in the CA Foundation exam.

View Official ICAI Syllabus

Exam Strategy Tip

This topic carries 4-6 Marks weightage. Focus on understanding core concepts rather than memorizing.

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