Squaring a binomial

The question

Ana wrote (x + 5)² − 25 = x² + 10x + 25. Which is correct?

(x + 5)² − 25

(x + 5)² − 25=x² + 10x + 25 − 25

(x + 5)² − 25=x² + 10x

they wrote:x² + 10x + 25

Do the step yourself first, then compare with their line.
On your own, writing every step: (x + 5)² − 25 becomes x² + 10x + 25 − 25.
Tidy that up and it is x² + 10x.
Now compare. They wrote x² + 10x + 25, and the squared constant was never taken away again — so the correct answer is x² + 10x.

How it works.

01
Do the step yourself first, then compare with their line.
02
On your own, writing every step: (x + 5)² − 25 becomes x² + 10x + 25 − 25.
03
Tidy that up and it is x² + 10x.
04
Now compare. They wrote x² + 10x + 25, and the squared constant was never taken away again — so the correct answer is x² + 10x.