What is the expression in factored form 16x2 - 25?

16x^2 - 25

Recognise that both 16 and 25 are squared numbers, 16 = 4^(2) & 25 = 5^(2)

Substituting

4^(2)x^(2) - 5^(2) = >

(4x)^(2) - 5^(2)

We now have two squared terms with a negative between them.

NB two squared terms with positive does NOT factor.

Factoring

(4x - 5)(4x + 5)