Factories the following expression-

l² – 16l + 64

In the given expression

1^st and last terms are perfect square

⇒ l² = l × l

⇒ 64 = 8 × 8

And the middle expression is in form of 2ab

16l = 2 × 8 × l

∴ l × l + 2 × 8 × l + 8 × 8

Gives (a-b)² = a²-2ab + b²

⇒ In l² + 16l + 64

a = l and b = 8;

∴ l² + 16l + 64 = (l + 8)²

Hence the factors of l² + 16l + 64 are (l + 8) and (l + 8)