390. 1) (2x²- 5xy + y²)·2xy; 2) (-6a²-7ab - b²)·(-3ab); 3) (5m²+10mn -4n²)·(-½ mn); 4) (-1-p²-¾ pq+q²)·(-2pq).

Решение:

1. \( (2x^2-5xy+y^2)(2xy) = 4x^3y-10x^2y^2+2xy^3 \)
2. \( (-6a^2-7ab-b^2)(-3ab) = 18a^3b+21a^2b^2+3ab^3 \)
3. \( (5m^2+10mn-4n^2)(-\frac{1}{2} mn) = -\frac{5}{2}m^3n - 5m^2n^2 + 2mn^3 \)
4. \( (-1-p^2-\frac{3}{4}pq+q^2)(-2pq) = 2pq + 2p^3q + \frac{3}{2}pq^2 - 2q^3p \)

Ответ: 1) \( 4x^3y-10x^2y^2+2xy^3 \); 2) \( 18a^3b+21a^2b^2+3ab^3 \); 3) \( -\frac{5}{2}m^3n - 5m^2n^2 + 2mn^3 \); 4) \( 2pq + 2p^3q + \frac{3}{2}pq^2 - 2q^3p \).