Ответ:с^2+с^3-5с-15

6х^2+12ху+4ху+8у^2

6а^2-8а+3а-4

Объяснение:

1) (c - 5) (c + 3) = c^2 + 3c - 5c - 15 = c^2 - 2c - 15

2) (3x + 2y) (2x + 4y) = 6x^2 + 12xy + 4xy + 8y^2 = 6x^2 + 16xy + 8y^2

3) (2a + 1) (3a - 4) = 6a^2 - 8a + 3a - 4 = 6a^2 - 5a - 4

4) (b - 2) (b^2 - 3b + 6) = b^3 - 3b^2 + 6b - 2b^2 + 6b - 12 = b^3 - 5b^2 + 12b - 12