1.

-aba + a²b2ab² + 4 = -a²b + 2a³b³ + 4 =  a²b * (- 1 +  2ab²) + 4

a = 2; b = ½

4 * ½ * (-1 + 2 * 2 * ¼) + 4 = 2 * (- 1 + 1) + 4 =  2 * 0 + 4 = 4

2.

b²5ab – 5a5a²b = 5ab * (b² – 5a²)

a = 1/5;  b = - 2

5 * 1/5 * (-2) * ((-2)² – 5 * (1/5)²) = - 2 * (4 – 1/5) = - 2 * 19/5 = - 38/5 = 

= - 7  3/5    (7 цеых и 3/5)

3.

x²yxy - xy²xy + xy = xy * (x²y – xy² + 1)

x = - 3; y = 2

(- 3) * 2 * ((-3)² * 2 – (-3) * 2² + 1) = - 6 * (9 * 2 + 3 * 4 + 1) =  - 6 * (18 + 12 + 1) = - 6 * 31 = - 186

4.

xy²x²y - xyxy  =  x²y² * (xy – 1)

x = - 2; y = 3

(- 2)² * 3² * ((-2) * 3 – 1) = 4 * 9 * (- 6 - 1) = - 36 * 7 = - 252