Bài 1:
a) \(A=x^2\left(x-y^2\right)-xy\left(1-xy\right)-x^3\)
\(A=x^3-x^2y^2-xy+x^2y^2-x^3\)
\(A=\left(x^3-x^3\right)+\left(-x^2y^2+x^2y^2\right)-xy\)
\(A=-xy\)
b) \(B=x\left(x+3y+1\right)-2y\left(x-1\right)-\left(y+x+1\right)x\)
\(B=\left(x^2+3xy+x\right)-\left(2xy-2y\right)-\left(xy+x^2+x\right)\)
\(B=x^2+3xy+x-2xy+2y-xy-x^2-x\)
\(B=\left(x^2-x^2\right)+\left(3xy-2xy-xy\right)+\left(x-x\right)+2y\)
\(B=2y\)
2:
a: C=A+B
\(=4x^2+3y^2-5xy+3x^2+2y^2+2x^2y^2\)
\(=7x^2+5y^2-5xy+2x^2y^2\)
b: C+A=B
=>C=B-A
\(=3x^2+2y^2+2x^2y^2-4x^2-3y^2+5xy\)
\(=-x^2-y^2+2x^2y^2+5xy\)
