Answer:
(y - 5)²
Explanation:
y² - 10y + 25
consider the factors of the constant term (+ 25) which sum to give the coefficient of the y- term (- 10)
the factors are - 5 and - 5 , since
- 5 × - 5 = + 25 and - 5 - 5 = - 10 , then
y² - 10y + 25
= (y - 5)(y - 5)
= (y - 5)²