(i) x2+y2+z2−xy+x+yz by x+y−z
(ii) x2+4y2+z2+2xy+xz−2yz by x−2y−z
(iii) x2+4y2+2xy−3x+6y+9 by x−2y+3
(iv) 9x2+25y2+15xy+2x−20y+16 by 3x−5y+4
(i)(x2+y2+z2−xy+yz+zx)by(x+y−z)−x3+y3−z3+3xyz(ii)(x2+4y2+z2+2xy+xz−2yz)by(x−2y−z)=(x−2y−z)[x2+(−2y)2+(−z)2−x×(−2y)−(−2y)(z)−(−z)(x)]=x3+(−2y)3+(−z)3−3x(−2y)(−z)=x3−8y3−z3−6xyz(iii)x2+4y2+2xy−3x+6y+9byx−2y+3=(x−2y+3)(x2+4y2+9+2xy+5y−3x)=(x)3+(−2y)2+(3)3−3×x×(−2y)×3=x3−8y3+27+18xy(iv)9x2+14y2+15xy+12x−20y+16by3x−5y+4=(3x−5y+4)[(3x)2+(−5y)2+(4)2−3x×(−5y)(−5y×4)−(4×3x)]=(3x)3+(−5y)3+(4)3−3×3x(−5y)×4=27x3−125y3+64+180xy