64-25v2

Rewrite 64 as 82.

82-25v2

Rewrite 25v2 as (5v)2.

82-(5v)2

Since both terms are perfect squares, factor using the difference of squares formula, a2-b2=(a+b)(a-b) where a=8 and b=5v.

(8+5v)(8-(5v))

Multiply 5 by -1.

(8+5v)(8-5v)

Factor 64-25v^2