Question

[dan nguyen chi]

Bài 1: Làm tính nhân:

a) 3x(5x² - 2x - 1) ;

b) (x² + 2xy - 3)(-xy) ;

c) \(\dfrac{1}{2}\)x²y(2x³ - \(\dfrac{2}{5}\)xy² - 1).

Bài 2: Rút gọn các biểu thức sau:

a) x(2x² - 3) - x²(5x + 1) + x² ;

b) 3x(x - 2) - 5x(1 - x) - 8(x² - 3) ;

c) \(\dfrac{1}{2}\)x²(6x - 3) - x (x² + \(\dfrac{1}{2}\)) + \(\dfrac{1}{2}\)(x + 4).

Answer 1

[Đức Hiếu]

Bài 1:

a,\(3x\left(5x^2-2x-1\right)\)

\(=3x.5x^2-3x.2x-3x=15x^3-6x^2-3x\)

b,\(\left(x^2+2xy-3\right)\left(-xy\right)\)

\(=x^2.\left(-xy\right)+2xy.\left(-xy\right)-3.\left(-xy\right)\)

\(=-x^3y-2x^2y^2+3xy\)

c,\(\dfrac{1}{2}x^2y\left(2x^3-\dfrac{2}{5}xy^2-1\right)\)

\(=\dfrac{1}{2}x^2y.\left(2x^3\right)-\dfrac{1}{2}x^2y.\dfrac{2}{5}xy^2-\dfrac{1}{2}x^2y\)

\(=x^5y-\dfrac{1}{5}x^3y^3-\dfrac{1}{2}x^2y\)

Chúc bạn học tốt!!!

Answer 2

[Nguyễn Trần Thành Đạt]

Bài 1:

a) \(3x\left(5x^2-2x-1\right)\\ =15x^3-6x^2-3x\)

b) \(\left(x^2+2xy-3\right)\left(-xy\right)\\ =-x^3y-2x^2y+3xy\)

c) \(\dfrac{1}{2}x^2y\left(2x^3-\dfrac{2}{5}xy^2-1\right)\\ =x^5y-\dfrac{1}{5}x^3y^3-\dfrac{1}{2}x^2y\)