EquationsMCQPYQ Nov 19Question 1105 of 221
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Roots of the quadratic equation x3+9x2x9=0\displaystyle x^3 + 9x^2 - x - 9 = 0.

Options

A1,2,3\displaystyle 1, 2, 3
B1,1,9\displaystyle 1, -1, -9
C2,3,9\displaystyle 2, 3, 9
D1,3,9\displaystyle 1, 3, 9
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Correct Answer

Option c2,3,9\displaystyle 2, 3, 9

All Options:

  • A1,2,3\displaystyle 1, 2, 3
  • B1,1,9\displaystyle 1, -1, -9
  • C2,3,9\displaystyle 2, 3, 9
  • D1,3,9\displaystyle 1, 3, 9

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Detailed Solution & Explanation

Let us solve the cubic equation x3+9x2x9=0\displaystyle x^3 + 9x^2 - x - 9 = 0 by factoring by grouping:
x3+9x2x9=0x^3 + 9x^2 - x - 9 = 0
x2(x+9)1(x+9)=0x^2(x + 9) - 1(x + 9) = 0
(x21)(x+9)=0(x^2 - 1)(x + 9) = 0
(x1)(x+1)(x+9)=0(x - 1)(x + 1)(x + 9) = 0

This gives the three roots:
x1=0    x=1\displaystyle x - 1 = 0 \implies x = 1
x+1=0    x=1\displaystyle x + 1 = 0 \implies x = -1
x+9=0    x=9\displaystyle x + 9 = 0 \implies x = -9

Thus, the roots are 1,1,9\displaystyle 1, -1, -9, which corresponds exactly to Option (b). (Note: The official key marks the correct option as Option (c) due to a typographical mistake, but mathematically Option (b) is the correct set of roots).

Hence, the correct option is **Option (b)**.

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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