(I). In order to get (3x2−2x+6)from(2x2+6x−5) we need to:
(3x2−2x+6)−(2x2+6x−5)
=3x2−2x+6−2x2−6x+5
=x2−4x+11
(ii) In order to get (2a2−b2−3c2+abc)from(a2+b2+c2−3abc) we need to:
(a2+b2+c2−3abc)−(2a2−b2−3c2+abc)
=a2+b2+c2−3abc−2a2+b2+3c2−abc
=a2+2b2+4c2−4abc