Bài 1:
`a)(x+1)(x-1)(x²+1)`
`=(x²-1)(x²+1)`
`=(x^2)^2-1^2`
`=x^4-1`
`b)1/2x²y²(2x+y)(2x-y)`
`=1/2x²y²[(2x)²-y²]`
`=1/2x²y²(4x²-y²)`
`=2x^4y²-1/2x²y^4`
`c)(2x+3)²+(2x-3)²`
`=(2x)²+2.2x.3+3²+(2x)²-2.2x.3+3²`
`=4x²+12x+9+4x²-12x+9`
`=(4x²+4x²)+(12x-12x)+(9+9)`
`=8x²+18`
`d)(4x+y)²-(4x-y)²`
`=[(4x+y)+(4x-y)][(4x+y)-(4x-y)]`
`=(4x+y+4x-y)(4x+y-4x+y)`
`=8x.2y`
`=16xy`
`e)(x+y)²+(x-y)²`
`=x²+2xy+y²+x²-2xy+y²`
`=(x²+x²)+(2xy-2xy)+(y²+y²)`
`=2x²+2y²`
`g)(x+y)²+2(x+y)(x-y)+(x-y)²`
`=(x+y+x-y)²`
`=(2x)²`
`=4x²`
Bài 2:
`a)x^2y^4+2xy^2+1`
`=(xy^2)^2+2.xy².1+1²`
`=(xy^2+1)^2`
`b)(5-x)²`
`=5²-2.5.x+x²`
`=25-10x+x²`
`c)9x²-12x+4`
`=(3x)²-2.3x.2+2²`
`=(3x-2)²`
`d)(xy+2)^2`
`=(xy)²+2.xy.2+2²`
`=x²y²+4xy+4`
