Đáp án:
Bài `1:`
`a,5x^2+3x-1`
`x=-1` ta có:
`5.(-1)^2+3.(-1)-1=5.1+(-3)-1=5-3-1=1`
`b,3x-5y+2`
`x=2;y=1` ta có:
`3.2-5.1+2=6-5+2=1+2=3`
Bài `2:`
`a,x^2+5x^2+(-4x^2)=(1+5-4)x^2=2x^2`
`b,1/2x^2y+x^2y+(-1/3x^2y)=(1/2+1-1/3)x^2y=7/6x^2y`
Bài `3:`
`a,4xy.(-2x^2y)=(4. -2).(x.x^2).(y.y)=-8x^3y^2`
`b,2xy.(3xy^2)^2=2xy.9x^2y^4=(2.9).(x.x^2).(y.y^4)=18x^3y^5`
