Final answer:
The term missing to complete the square for the expression x² - 10x is +25, resulting in (x - 5)².
Step-by-step explanation:
Completing the square involves finding a constant term to add to a quadratic expression of the form x² + bx so that it can be expressed as the square of a binomial, (x + d)². The formula to calculate this term is (b/2)². Therefore, for the expression x² - 10x, you would use b = -10 and calculate (-10/2)² which is 25. Hence, the term missing to complete the square for the expression x² - 10x is +25, resulting in (x - 5)².