Answer:
a = 4, b = 5
Step-by-step explanation:
x² - 8x + 21
Using the method of completing the square
add/subtract ( half the coefficient of the x- term )² to x² - 8x
x² + 2(- 4)x + 16 - 16 + 21
= (x - 4)² + 5 ← in the form (x - a)² + b
with a = 4 and b = 5
