The sum of x2 – 5xy + 2y2 and y2 – 2xy – 3x2
= (x2 – 5xy + 2y2) (y –2xy – 3x2)
= (x2 – 3x2) + ( – 5xy – 2xy) + (2y2 + y2)
= – 2x2 – 7xy + 3y2 ………………….(1)
The sum of 6x2 – 8xy – y2 and
2xy – 2y2 – x2 = (6x2 – 8xy – y2) + (2xy – 2y2 – x2)
= (6x2 – x2) + ( – 8xy + 2xy) + (-y2 – 2y2)
= 5x2 – 6xy – 3y2 ………………. (2)
From (1) and (2)
(2) – (1)= (5x2 – 6xy – 3y2) – ( – 2x2 – 7xy + 3y2)
= 5x2 – 6xy – 3y2 + 2x2 + 7xy – 3y2
= (5x2 + 2x2) + ( – 6xy + 7xy) + ( – 3y2 – 3y2)
= 7x2 + xy – 6y2