1.x^2+x-1/2x^2-1+x-1=(1/2)x^2+x-1.
2.x^2+2x+3/1x^2-9x-12=4x^2-7x-12.
3.-x^2+9x-1/20x^2-7x+12=(21/20)x^2+2x+12.
4.y^2-2y+xy/1-x-y+1=y^2-3y+xy-x+1