Đáp án + Giải thích các bước giải:
`2A+3B-5C`
`=2(4x^2-5xy+2x-5y+3y^2)+3(-3x^2+2xy-5y+y^2)-5(-x^2+3xy+2x+2y^2)`
`=(2.4x^2-2.5xy+2.2x-2.5y+2.3y^2)+(-3x^2 .3+2xy.3-5y.3+y^2 .3)-(-x^2 .5+3xy.5+2x.5+2y^2 .5)`
`=(8x^2-10xy+4x-10y+6y^2)+(-9x^2+6xy-15y+3y^2)-(-5x^2+15xy+10x+10y^2)`
`=8x^2-10xy+4x-10y+6y^2-9x^2+6xy-15y+3y^2+5x^2-15xy-10x-10y^2`
`=(8x^2-9x^2+5x^2)-(10xy-6xy+15xy)+(4x-10x)-(10y+15y)+(6y^2+3y^2-10y^2)`
`=4x^2-19xy-6x-25y-y^2`
Vậy `2A+3B-5C=4x^2-19xy-6x-25y-y^2`