Question

 

Answer 1

a: A+B-C

=16x^4-8x^3y+7x^2y^2-9y^4-15x^4+3x^3y-5x^2y^2-6y^4-C

=x^4-5x^3y+2x^2y^2-15y^4-5x^3y-3x^2y^2-17y^4-1

=x^4-17y^4-10x^3y-x^2y^2-1

b: A-C+B

=A+B-C

=x^4-17y^4-10x^3y-x^2y^2-1