16a^2 - 81 = (4a)^2 - 9^2 = (4a - 9)(4a + 9)-формула разность квадратов
x^2 - 10x + 25 =( x - 5)^2 - формула квадрат разности
3(x - 1) + y( x - 1) = ( x - 1) ( 3 + y)
2a^2 - 4ab + 2b^2 = 2(a^2 - 2ab + b^2) = 2(a - b)^2
(2 - 3n)^2 - 9n^4 = ( 2 - 3n)^2 - (3n^2)^2 = (2 - 3n - 3n^2)(2 - 3n + 3n^2)
( a - 5)^2 + 2(5 - a) + 1 = ((a - 5)^2 - 2(a - 5)) + 1=( (a - 5)(a - 5 - 2)) + 1 =
= (a - 5)(a - 7) + 1 = a^2 - 12a + 35 + 1 = a^2 - 12a + 36 = ( a - 6)^2