y = x² - 10x + 8 Multiply coefficient of x, which is -10, by, getting -5. Square -5, getting (-5)² = +25. Add 25 - 25 (which is really zero) to the right side after the -10x y = x² - 10x + 25 - 25 + 8 Factor the first three terms on the right sides: y = (x - 5)(x - 5) - 25 + 8 Write (x - 5)(x - 5) as (x - 5)², and write -25 + 8 as -17 y = (x - 5)² - 17 That's it. Edwin