This can be factored as a difference of two squares. When you have a difference of two squares (a² - b²), it will factor out into (a + b) (a - b).
(x² - r²)
(x + r)(x - r)
You can multiply the two groups to double check it.
(x + r)(x - r)
x² - rx + rx - r²
x² - r²
