Question

设A=X的二次方-（减号）XY B=XY+Y的二次方 求 A+B 3A-2B

Answer 1

设A=X的二次方-（减号）XY B=XY+Y的二次方

A=X^2-XY B=XY+Y^2

A+B=X^2-XY + XY+Y^2 =X^2+Y^2

3A-2B =3(X^2-XY )-2( XY+Y^2)=3X^2-3XY-2XY-2Y^2=3X^2-5XY-2Y^2