Bài `10`:

`1) P+(x^2 -2y^2)= x^2 -y^2+3y^2-1`

`=> P = x^2 -y^2+3y^2  -1-x^2 +2y^2`

`=> P = x^2 -x^2 -y^2 +2y^2 +3y^2 -1`

`=> P = (1-1).x^2 +(-1 +2 +3).y^2 -1`

`=> P = 4y^2 -1`

Vậy `bbP = 4y^2 -1`

`2)Q- ( 5x^2 -xyz)= xy +2x^2 -3xyz +5`

`=> Q = xy +2x^2 -3xyz +5 +5x^2 +xyz`

`=> Q = 2x^2 +5x^2 -3xy -xyz+xy +5`

`=> Q = (2+5).x^2 + (-3 -1).xyz +xy +5`

`=> Q = 7x^2 -4xyz +xy +5`

Vậy `bbQ = 7x^2 -4xyz +xy +5`.