390. 1) (2x²-5xy+y²)·2xy; 2) (-6a²-7ab-b²)·(-3ab);

Решение:

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