Math Problem Statement

2x^3+3x^2−1=0

Solution

You provided the equation:

2x3+3x21=02x^3 + 3x^2 - 1 = 0

This is a cubic equation. Let's explore possible methods for solving it.

Step 1: Try Rational Root Theorem

The Rational Root Theorem helps identify potential rational solutions of the form pq\frac{p}{q}, where:

  • pp is a factor of the constant term (here, 1-1),
  • qq is a factor of the leading coefficient (here, 22).

Possible values for xx are:

x=±1,±12x = \pm 1, \pm \frac{1}{2}

Step 2: Test possible values of xx

We will substitute these values into the equation to check for valid solutions.

Test x=1x = 1:

2(1)3+3(1)21=2+31=402(1)^3 + 3(1)^2 - 1 = 2 + 3 - 1 = 4 \neq 0 So, x=1x = 1 is not a solution.

Test x=1x = -1:

2(1)3+3(1)21=2(1)+3(1)1=2+31=02(-1)^3 + 3(-1)^2 - 1 = 2(-1) + 3(1) - 1 = -2 + 3 - 1 = 0 So, x=1x = -1 is a solution.

Step 3: Factor the cubic equation

Since x=1x = -1 is a solution, we can now factor the cubic equation using (x+1)(x + 1) as one of the factors.

Using synthetic division or polynomial long division, divide 2x3+3x212x^3 + 3x^2 - 1 by (x+1)(x + 1):

2x3+3x21x+1=2x2+x1\frac{2x^3 + 3x^2 - 1}{x + 1} = 2x^2 + x - 1

So, the factored form of the equation is:

(2x2+x1)(x+1)=0(2x^2 + x - 1)(x + 1) = 0

Step 4: Solve the quadratic equation

Now solve the quadratic 2x2+x1=02x^2 + x - 1 = 0 using the quadratic formula:

x=b±b24ac2ax = \frac{-b \pm \sqrt{b^2 - 4ac}}{2a}

For 2x2+x1=02x^2 + x - 1 = 0, a=2a = 2, b=1b = 1, and c=1c = -1. Substituting these values into the quadratic formula:

x=1±124(2)(1)2(2)x = \frac{-1 \pm \sqrt{1^2 - 4(2)(-1)}}{2(2)} x=1±1+84x = \frac{-1 \pm \sqrt{1 + 8}}{4} x=1±94x = \frac{-1 \pm \sqrt{9}}{4} x=1±34x = \frac{-1 \pm 3}{4}

So, the two solutions are:

x=1+34=24=12x = \frac{-1 + 3}{4} = \frac{2}{4} = \frac{1}{2} x=134=44=1x = \frac{-1 - 3}{4} = \frac{-4}{4} = -1

Step 5: Conclusion

The full set of solutions for the cubic equation 2x3+3x21=02x^3 + 3x^2 - 1 = 0 is:

[ x = -

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Math Problem Analysis

Mathematical Concepts

Algebra
Cubic Equations
Rational Root Theorem
Quadratic Equations

Formulas

Cubic equation standard form: ax^3 + bx^2 + cx + d = 0
Rational Root Theorem: possible rational roots = ±p/q
Quadratic formula: x = (-b ± √(b^2 - 4ac)) / 2a

Theorems

Rational Root Theorem

Suitable Grade Level

Grades 9-12