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Factor x^2 - 25

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

Step by step

The question

Question: factor x² − 25.

Factor means: write it as a times, with brackets.

x2 − 25

1 Two squares

This is one square take away another square.

x² is x squared.

25 is 5 squared.

A square minus a square is the plus bracket times the minus bracket.

a² − b² = (a + b)(a − b)
x2 = (x)²
25 = 5²

So we get (x + 5)(x − 5).

= (x + 5)(x − 5)

2 Check

Let's check: we multiply it back out.

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

Check: (x + 5)(x − 5) = x2 − 5x + 5x − 25
= x2 − 25

We get x² − 25 again.

So (x + 5)(x − 5) is right!

Let's look back.

First: two squares.

Last: check.

Answer
= (x + 5)(x − 5)

Your turn

Try this one yourself, then check:

Factor x2 − 49
Show the answer
(x + 7)(x − 7)

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