Bài 1:
`a)x²y(x²-2xy+2/3y)`
`=x²y.x²-x²y.2xy+x²y. 2/3y`
`=x^4y-2x³y²+2/3x²y²`
`b)(x²+1)(5-x)`
`=x².5-x².x+1.5-1.x`
`=5x²-x³+5-x`
`c)(x-2)(x-x²+4)`
`=x.x-x.x²+x.4-2.x+2.x²-2.4`
`=x²-x³+4x-2x+2x²-8`
`=-x³+(x²+2x²)+(4x-2x)-8`
`=-x³+3x²+2x-8`
`d)(x-2)(x-x²+4)`
`=x.x-x.x²+x.4-2.x+2.x²-2.4`
`=x²-x³+4x-2x+2x²-8`
`=-x³+(x²+2x²)+(4x-2x)-8`
`=-x³+3x²+2x-8`
Bài 2:
`a)(x-2y)²`
`=x²-2.x.2y+(2y)²`
`=x²-4y+4y²`
`b)(x-2)(x²+2x+4)`
`=x³-2³`
`=x³-8`
`c)(2x²+3)²`
`=(2x²)^2+2.2x².3+3²`
`=4x^4+12x²+9`
`d)(2x-1)³`
`=(2x)^3-3.(2x)².1+3.2x.1²-1³`
`=8x³-12x²+6x-1`
