Bài 2:
`a)x³+3x²+3x+1`
`=x³+3.x².1+3.x.1²+1³`
`=(x+1)³`
`b)27y³-9y²+y-1/27`
`=(3y)³-3.(3y)². 1/3+3.3y. (1/3)^2-(1/3)^3`
`=(3y-1/3)^3`
`c)8x^6+12x^4y+6x²y²+y³`
`=(2x²)^3+3.(2x²)^2 .y+3.2x².y²+y³`
`=(2x²+y)³`
`d)(x+y)³(x-y)³`
`=[(x+y)(x-y)]³`
`=(x²-xy+xy-y²)^3`
`=(x²-y²)^3`
Bài 3:
`a)1,24²-0,24²`
`=(1,24+0,24)(1,24-0,24)`
`=1,48.1`
`=1,48`
`b)1/8-8x³`
`=(1/2)^3-(2x)³`
`=(1/2-2x)[(1/2)^2+1/2 .2x+(2x)²]`
`=(1/2-2x)(1/4+x+4x²)`
`c)x²-x+1/4`
`=x²-2.x. 1/2+(1/2)^2`
`=(x-1/2)^2`
`d)x²+x+1/4`
`=x²+2.x. 1/2+(1/2)^2`
`=(x+1/2)^2`
