b²-16 = (b-4)(b+4)

25a²-81y² = (5a-9y)(5a+9y)

x²-6x+9 = (x-3)²

4y³-y = y(4y²-1) = y(2y-1)(2y+1)

(a-5b)²(a+5b)² = (a²-10b+25)(a²+10b+25) = a⁴-50a²+625

a²-12a+36 = (a-6)²; (506-6)² = 500² = 250000

x³+y³+x²-xy+y² = (x+y)(x²-xy+y²)+(x²-xy+y²) = (x²-xy+y²)(x+y+1)

Есть такая формула. a²+b²=(a+b)²-2ab=(a-b)²+2ab. Ей и воспользуемся.

4x²+9y² = (2x+3y)²-2*2x*3y = (2x+3y)²-12xy;

18²-12*6 = 324-72 = 252.

b²-16 = (b-4)(b+4)

25a²-81y² = (5a-9y)(5a+9y)

x²-6x+9 = (x-3)²

4y³-y = y(4y²-1) = y(2y-1)(2y+1)

(a-5b)²(a+5b)² = (a²-10b+25)(a²+10b+25) = a⁴-50a²+625

a²-12a+36 = (a-6)²; (506-6)² = 500² = 250000

x³+y³+x²-xy+y² = (x+y)(x²-xy+y²)+(x²-xy+y²) = (x²-xy+y²)(x+y+1)

смог только это