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Factor x^3 + 5x^2 + x + 5

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

Step by step

The question

Question: factor x³ + 5x² + x + 5.

There are four terms.

So we factor them in pairs.

This is called grouping.

x3 + 5x2 + x + 5

1 Group in pairs

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

= (x3 + 5x2) + (x + 5)

From the first pair we take out x².

From the second pair we take out 1.

Nothing else is common, so it is just 1.

Both leave the same bracket, x + 5.

(x3 + 5x2) = x2(x + 5)
(x + 5) = 1(x + 5)

Now both parts have x + 5 in them.

= x2(x + 5) + 1(x + 5)

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 + 5 is in both parts, so we take it out once.

What is left, x² + 1, goes in the other bracket.

ab + cb = b(a + c)

So we get (x + 5)(x² + 1).

= (x + 5)(x2 + 1)

3 Check

Let's check: we multiply it back out.

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

Check: (x + 5)(x2 + 1) = x3 + x + 5x2 + 5
= x3 + 5x2 + x + 5

We get x³ + 5x² + x + 5 again.

So the answer is right!

Let's look back.

First: group in pairs.

Then: same bracket out.

Last: check.

Answer
= (x + 5)(x2 + 1)

Your turn

Try this one yourself, then check:

Factor x3 + x2 + x + 1
Show the answer
(x + 1)(x2 + 1)

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