Answer:
y² - 100
Step-by-step explanation:
(y + 10)(y - 10)
Each term in the second factor is multiplied by each term in the first factor, that is
y(y - 10) + 10(y - 10) ← distribute parenthesis
= y² - 10y + 10y - 100 ← collect like terms
= y² - 100
