Answer:

(x - 5)²

Step-by-step explanation:

(a + b)² = (a² + 2ab + b²)

(a + b)² = (x² - 10x + 25)

a² = x²

a = x

b² = 25

b = ± 5

Since there's a minus (negative sign) in (2ab), we'll use - 5.

(a + b)² = (x - 5)²