Discussion about math, puzzles, games and fun. Useful symbols: ÷ × ½ √ ∞ ≠ ≤ ≥ ≈ ⇒ ± ∈ Δ θ ∴ ∑ ∫ π -¹ ² ³ °

You are not logged in.

- Topics: Active | Unanswered

Pages: **1**

**Oculus8596****Banned**- From: Great Lakes,Illinois
- Registered: 2024-09-18
- Posts: 126

Factor the polynomial completely.

x^6 + 2x^3 + 1

The best things in life are not always free.

Offline

**Bob****Administrator**- Registered: 2010-06-20
- Posts: 10,610

You might spot an immediate factorisation but if not here's how to force it.

Let y = x^3 and the expression becomes y^2 + 2y +1 which can be factored into two identical factors,.

Putting x back into one of those and you're down to a cubic. Substitute x = 1 and the expression is zero so x-1 nust be a factor. Extracting that leaves a quadratic which cannot be factored further.

Bob

Children are not defined by school ...........The Fonz

You cannot teach a man anything; you can only help him find it within himself..........Galileo Galilei

Sometimes I deliberately make mistakes, just to test you! …………….Bob

Offline

**Oculus8596****Banned**- From: Great Lakes,Illinois
- Registered: 2024-09-18
- Posts: 126

Bob wrote:

You might spot an immediate factorisation but if not here's how to force it.

Let y = x^3 and the expression becomes y^2 + 2y +1 which can be factored into two identical factors,.

Putting x back into one of those and you're down to a cubic. Substitute x = 1 and the expression is zero so x-1 nust be a factor. Extracting that leaves a quadratic which cannot be factored further.

Bob

Can x^6 be expressed as (x^3)^2?

I can then say y = x^3.

The given polynomial becomes y^2 + 2y + 1.

y^2 + 2y + 1 factors out to be (y + 1)(y + 1).

I can back-substitute to get (x^3 + 1)(x^3 + 1),which equals (x^3 + 1)^2.

Can the sum of cubes be applied to further factor x^3 + 1?

The best things in life are not always free.

Offline

**Bob****Administrator**- Registered: 2010-06-20
- Posts: 10,610

Consider x^3 + 1. The factor theorem can be used here. Set x = -1 and x^3 + 1 evaluates to zero. This means (x + 1) is a factor.

x^3 + 1 = (x+1)(x^2 -x +1)

Bob

Children are not defined by school ...........The Fonz

You cannot teach a man anything; you can only help him find it within himself..........Galileo Galilei

Sometimes I deliberately make mistakes, just to test you! …………….Bob

Offline

**Oculus8596****Banned**- From: Great Lakes,Illinois
- Registered: 2024-09-18
- Posts: 126

Bob wrote:

Consider x^3 + 1. The factor theorem can be used here. Set x = -1 and x^3 + 1 evaluates to zero. This means (x + 1) is a factor.

x^3 + 1 = (x+1)(x^2 -x +1)

Bob

The sum of cubes works just the same.

The best things in life are not always free.

Offline

Pages: **1**