Giải thích các bước giải:
a/. 2x. (x² + 5xy - 1)
= 2x³ + 10x²y - 2x
b/. (3xy - `(yz)/2`) .(- `5/3`xy²)
= 3xy . - `5/3`xy² + `(yz)/2`. `5/3`xy²
= - 5x²y³ + `5/6`xy³z
c/. (4x² - `3/2`xy + `1/4`)(- 10xy²)
= 4x² . (-10xy²) -`3/2`xy. (-10xy²) + `1/4`(- 10xy²)
= - 40x³y² + 15x²y³ - `5/2`xy²
d/. x.(1 - 3x)(4 - 3x) - (x - 4)(3x + 5)
= x.(4 - 3x - 12x + 9x²) - (3x² + 5x - 12x - 20)
= 4x - 3x² - 12x² + 9x³ - 3x² - 5x + 12x + 20
= 9x³ + (-3x² - 12x² - 3x²) + (4x - 5x + 12x) + 20
= 9x³ - 18x² + 11x + 20
