Question

subtract 7xy+5x²-7y²+3 from 7x²-8xy+3y²+5

Answer 1

answer is
$15xy - 2 {x}^{2} - 10 {y}^{2} - 2$

Answer 2

=7x^2- 8xy +3y^2 +5- (7xy+ 5x^2 - 7y^2+3)
=7x^2-8xy+ 3y^2+ 5- 7xy- 5x^2 +7y^2- 3
=7x^2-5x^2- 8xy- 7xy + 3y^2+7y^2+5- 3
=2x^2- 15xy +10y^2 + 2