Question

Thực hiện phép tính

a) (- 2x - 1)(2x ^ 2 - 1/2 * x + 2)
b) (5x ^ 2 - 2xy) - (6x ^ 2 + 9xy - y ^ 2)
c) 4x ^ 2 * y ^ 4 * (2x ^ 2 - xy) - 7x ^ 3 * y ^ 3 * (xy - y ^ 2) 

Answer 1

\(a,\left(-2x-1\right)\left(2x^2-\dfrac{1}{2}x+2\right)\\ =\left(2x+1\right)\left(\dfrac{1}{2}x-2x^2-2\right)\\ =2x\left(\dfrac{1}{2}x-2x^2-2\right)+\left(\dfrac{1}{2}x-2x^2-2\right)\\ =x^2-4x^3-4x+\dfrac{1}{2}x-2x^2-2\\ =-4x^3-x^2-\dfrac{7}{2}x-2\\ b,\left(5x^2-2xy\right)-\left(6x^2+9xy-y^2\right)\\ =5x^2-2xy-6x^2-9xy+y^2\\ =\left(-6y^2+y^2\right)+\left(-2xy-9xy\right)+5x^2\\ =-5y^2-11xy+5x^2\\ c,4x^2y^4\left(2x^2-xy\right)-7x^3y^3\left(xy-y^2\right)\\ =8x^4y^4-4x^3y^5-7x^4y^4+7x^3y^5\\ =x^4y^4+3x^3y^5\)