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Factor x^3 - 2x^2 + 5x - 10

Step by step, with the reason for every step · Factor by grouping · Algebra 1

Step by step

The question

Question: factor x³ − 2x² + 5x − 10.

There are four terms.

So we factor them in pairs.

This is called grouping.

x3 − 2x2 + 5x − 10

1 Group in pairs

We put the first two together, and the last two together.

= (x3 − 2x2) + (5x − 10)

From the first pair we take out x².

From the second pair we take out 5.

Both leave the same bracket, x − 2.

(x3 − 2x2) = x2(x − 2)
(5x − 10) = 5(x − 2)

Now both parts have x − 2 in them.

= x2(x − 2) + 5(x − 2)

Careful!

This is not the answer yet.

It is still two parts added.

Factored means one thing times another.

Careful: not done yet: still a + between two parts

2 Same bracket out

x − 2 is in both parts, so we take it out once.

What is left, x² + 5, goes in the other bracket.

ab + cb = b(a + c)

So we get (x − 2)(x² + 5).

= (x − 2)(x2 + 5)

3 Check

Let's check: we multiply it back out.

Each part of the first bracket times each part of the second.

Check: (x − 2)(x2 + 5) = x3 + 5x − 2x2 − 10
= x3 − 2x2 + 5x − 10

We get x³ − 2x² + 5x − 10 again.

So the answer is right!

Let's look back.

First: group in pairs.

Then: same bracket out.

Last: check.

Answer
= (x − 2)(x2 + 5)

Your turn

Try this one yourself, then check:

Factor x3 − 3x2 + 3x − 9
Show the answer
(x − 3)(x2 + 3)

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