Algebra • Step-by-Step

Solve x³ - 6x² + 11x - 6 = 0 with Steps

Solve the cubic equation x³ - 6x² + 11x - 6 = 0 step by step using synthetic division and factoring. Find roots x = 1, 2, and 3.

Problem Statement
x3−6x2+11x−6=0x^3 - 6x^2 + 11x - 6 = 0
Final Result
x=1,  2,  3x = 1, \; 2, \; 3

Formula Required: Rational Root Theorem & Synthetic Division

Test root x = 1, perform synthetic division to get x² - 5x + 6, then factor into (x - 2)(x - 3).

(x−1)(x−2)(x−3)=0(x - 1)(x - 2)(x - 3) = 0

Step-by-Step Solution

10 Steps
1

Write the equation in standard cubic form $ax^3 + bx^2 + cx + d = 0$.

x3−6x2+11x−6=0x^3 - 6x^2 + 11x - 6 = 0
2

Apply the Rational Root Theorem (a way to test for simple fraction/whole-number roots before trying harder methods). Testing $x = 1$, we find $f(1) = 0$, which proves that $(x - 1)$ is a factor by the Factor Theorem.

f(1)=f(1)=(1)3−6(1)2+11(1)−6=1−6+11−6=0  ✓  ⟹  (x−1) is a factor\begin{aligned} f(1) &= f(1) = (1)^3 - 6(1)^2 + 11(1) - 6 = 1 - 6 + 11 - 6 = 0 \;\checkmark \\[4pt] &\implies (x - 1) \text{ is a factor} \end{aligned}
3

Perform polynomial division (long division / synthetic division) of $x^3 - 6x^2 + 11x - 6$ by the factor $(x - 1)$ to obtain the reduced quotient $x^2 - 5x + 6$. Both Long Division (NCERT standard) and Synthetic Division (shortcut) are shown below:

Method 1: Long Division (NCERT)x2−5x+6x−1) x3−6x2+11x−6‾−(x3−x2)−−−−−−−−−−−−‾−5x2+11x−−−−−−−(−5x2+5x)−−−−−−‾6x−6−−−(6x−6)−−‾0Method 2: Synthetic Division (Shortcut)11−611−61−561−560\begin{aligned} &\textbf{Method 1: Long Division (NCERT)} \\[4pt] &\begin{array}{r} x^2 - 5x + 6 \\ x - 1{\overline{\smash{\big)}\, x^3 - 6x^2 + 11x - 6}} \\ \underline{-(x^3 - x^2)\phantom{------------}} \\ -5x^2 + 11x\phantom{------} \\ \underline{-(-5x^2 + 5x)\phantom{------}} \\ 6x - 6\phantom{--} \\ \underline{-(6x - 6)\phantom{--}} \\ 0 \end{array} \\[10pt] &\textbf{Method 2: Synthetic Division (Shortcut)} \\[4pt] &\begin{array}{c|rrrr} 1 & 1 & -6 & 11 & -6 \\ & & 1 & -5 & 6 \\ \hline & 1 & -5 & 6 & 0 \end{array} \end{aligned}
4

Express the cubic equation in factored form and isolate the quadratic factor.

(x−1)(x2−5x+6)=0  ⟹  x2−5x+6=0(x - 1)(x^2 - 5x + 6) = 0 \implies x^2 - 5x + 6 = 0
5

Calculate the discriminant $\Delta = b^2 - 4ac$ (tells us how many real roots exist) for $x^2 - 5x + 6 = 0$. Since $\Delta > 0$, there are two distinct real roots.

Δ=(−5)2−4(1)(6)=25−(24)=1\Delta = (-5)^2 - 4(1)(6) = 25 - (24) = 1
6

Apply the quadratic formula $x = \frac{-b \pm \sqrt{\Delta}}{2a}$.

x=−(−5)±12(1)=5±12x = \frac{-(-5) \pm \sqrt{1}}{2(1)} = \frac{5 \pm 1}{2}
7

Compute the two roots from the quadratic factor:

x2=5+12=3,x3=5−12=2x_2 = \frac{5 + 1}{2} = 3, \quad x_3 = \frac{5 - 1}{2} = 2
8

Final summary: All three real roots of the cubic equation are:

x=1,  3,  2x = 1, \; 3, \; 2
9

Combine into completely factored form and apply the Zero Factor Principle (if $a \cdot b = 0$, then $a = 0$ or $b = 0$).

(x−1)(x−3)(x−2)=0(x - 1)(x - 3)(x - 2) = 0
10

Structural Insight (Vieta's Relations for Cubics): Sum of roots = -b/a, Product of roots = -d/a.

∑xi=−ba=6,∏xi=−da=6\sum x_i = -\frac{b}{a} = 6, \quad \prod x_i = -\frac{d}{a} = 6

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Common Questions About Solve x³ - 6x² + 11x - 6 = 0

What are the roots of x³ - 6x² + 11x - 6 = 0?

x = 1, x = 2, and x = 3.

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