Math Problem Statement

x^3-5x^2-6x<0

Solution

We are tasked with solving the inequality:

x35x26x<0x^3 - 5x^2 - 6x < 0

Step 1: Factor the expression

First, factor the left-hand side:

x(x25x6)<0x(x^2 - 5x - 6) < 0

Next, factor the quadratic expression x25x6x^2 - 5x - 6:

x(x6)(x+1)<0x(x - 6)(x + 1) < 0

Step 2: Determine critical points

The critical points occur where the expression equals zero, which are:

x=0,x=6,x=1x = 0, \quad x = 6, \quad x = -1

These divide the real number line into four intervals: (,1),(1,0),(0,6),(6,)(-\infty, -1), \quad (-1, 0), \quad (0, 6), \quad (6, \infty)

Step 3: Test the sign in each interval

We now determine the sign of x(x6)(x+1)x(x - 6)(x + 1) in each of these intervals by picking a test point from each.

  1. For x(,1)x \in (-\infty, -1), take x=2x = -2: (2)((2)6)((2)+1)=(2)(8)(1)=16<0(-2)((-2) - 6)((-2) + 1) = (-2)(-8)(-1) = -16 < 0
  2. For x(1,0)x \in (-1, 0), take x=12x = -\frac{1}{2}: (12)(126)(12+1)=(12)(6.5)(0.5)>0\left(-\frac{1}{2}\right)\left(-\frac{1}{2} - 6\right)\left(-\frac{1}{2} + 1\right) = \left(-\frac{1}{2}\right)(-6.5)(0.5) > 0
  3. For x(0,6)x \in (0, 6), take x=1x = 1: (1)(16)(1+1)=1(5)(2)=10<0(1)(1 - 6)(1 + 1) = 1(-5)(2) = -10 < 0
  4. For x(6,)x \in (6, \infty), take x=7x = 7: (7)(76)(7+1)=(7)(1)(8)=56>0(7)(7 - 6)(7 + 1) = (7)(1)(8) = 56 > 0

Step 4: Solution

The inequality is satisfied when the expression is negative, which occurs in the intervals:

(,1)(0,6)(-\infty, -1) \cup (0, 6)

Since the inequality is strict (i.e., <0< 0 and not 0\leq 0), the critical points x=1x = -1, x=0x = 0, and x=6x = 6 are not included.

Thus, the solution is:

x(,1)(0,6)x \in (-\infty, -1) \cup (0, 6)

Would you like more details or have any questions?

Here are some related questions:

  1. How would the solution change if the inequality were 0\leq 0?
  2. How do you factor quadratic expressions systematically?
  3. What is the graphical interpretation of this inequality?
  4. How do you solve inequalities involving higher powers of xx?
  5. What if the inequality were x35x26x>0x^3 - 5x^2 - 6x > 0?

Tip: When solving inequalities, always check the sign in each interval created by the critical points.

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Math Problem Analysis

Mathematical Concepts

Algebra
Inequalities
Factoring
Polynomial Functions

Formulas

Factoring: x(x - 6)(x + 1) = 0

Theorems

Sign Analysis of Polynomial Functions
Zero Product Property

Suitable Grade Level

Grades 9-12