1) ( 2x + 1 ) ( x + 4 )

1) (2 * x + 1) * (x + 4) = 2 * x * x + 2 * x * 4 + 1 * x + 1 * 4 = 2 * x² + 8 * x + x + 4 = 2 * x² + 9 * x + 4; 

2) (2 * x + 3) * (5 * x - 4) = 2 * x * 5 * x + 2 * x * (- 4) + 3 * 5 * x + 3 * (- 4) = 10 * x² - 8 * x + 15 * x - 12 = 10 * x² + 7 * x - 12;

3) (3 * x - 2) * (2 * a - 1) = 6 * a * x - 3 * x - 4 * a + 2;

4) (5 * a - 3 * b) * (4 * a - b) = 20 * a² - 5 * a * b - 12 * a * b + 3 * b² = 20 * a² - 17 * a * b + 3 * b²;

5) (2 * m + 3 * n) * (2 * m - 5 * n) = 4 * m² - 10 * n * m + 6 * n * m - 15 * n² = 4 * m² - 4 * n * m - 15 * n²;

6) (3 * x + 2 * y) * (x - y) = 3 * x² - 3 * x * y + 2 * x * y - 2 * y² = 3 * x² - x * y - 2 * y²; 

7) (5 * b - 4 * c) * (2 * b - 2 * c) = 10 * b² - 10 * b * c - 8 * b * c + 8 * c² = 10 * b² - 18 * b * c + 8 * c²; 

8) (p - 3 * q) * (8 * p + 5 * q) = 8 * p² + 5 * p * q - 24 * p * q - 15 * q² = 8 * p² - 19 * p * q - 15 * q²;