`***`Lời giải`***`
a)
`(x+y)^2+(x-y)^2`
`=x^2+2xy+y^2+x^2-2xy+y^2`
`=(x^2+x^2)+(y^2+y^2)+(2xy-2xy)`
`=2x^2+2y^2`
b)
`2(x-y)(x+y)+(x+y)^2+(x-y)^2`
`=2(x^2-y^2)+x^2+2xy+y^2+x^2-2xy+y^2`
`=2x^2-2y^2+x^2+2xy+y^2+x^2-2xy+y^2`
`=(2x^2+x^2+x^2)+(y^2+y^2-2y^2)+(2xy-2xy)`
`=4x^2`
c)
`5(2x-1)^2+4(x-1)(x+3)-2(5-3x)^2`
`=5(4x^2-4x+1)+4(x^2+3x-x-3)-2(25-30x+9x^2)`
`=20x^2-20x+5+4(x^2+2x-3)-2(25-30x+9x^2)`
`=20x^2-20x+5+4x^2+8x-12-50+60x-18x^2`
`=6x^2+48-57`
