We will expand the factored form of (x − 9)(x − 1) into the same form as x² − 10x + 9 to show they are equal.
Distribute and multipy out:
(x − 9)(x − 1)
x * x = x²
x * -1 = -x
x * -9 = -9x
-9 * -1 = 9
Add together:
x² + -x + -9x + 9
x² − 10x + 9
Use the Reflexive property:
x² − 10x + 9 = x² − 10x + 9 ✓
