Math Is Fun Forum

mathxyz

Member

From: Brooklyn, NY

Registered: 2024-02-24

Posts: 1,053

Factor Difference of Cubes

Factor 27 - 8x^3.

Problem 36; page 57.

I will use formula 5 on page 44.

(x - a)(x^2 + ax + a^2)

Let 27 be 3^3. This means a = 3 in the formula.

Let 8x^3 be (2x)^3.

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

27 - 8x^3 = (2x - 3)(2x^2 - 3x + 9)

You say?

Bob

Administrator

Registered: 2010-06-20

Posts: 10,627

Re: Factor Difference of Cubes

Let 27 be 3^3. This means a = 3 in the formula.

Let 8x^3 be (2x)^3.

Good

But then

(2x - 3)[(2x)^2 - 3(2x) + 3^2]

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

mathxyz

Member

From: Brooklyn, NY

Registered: 2024-02-24

Posts: 1,053

Re: Factor Difference of Cubes

Let 27 be 3^3. This means a = 3 in the formula.

Let 8x^3 be (2x)^3.

Good

But then

(2x - 3)[(2x)^2 - 3(2x) + 3^2]

Bob

Oh yes. I forgot the final step.