Bài 14:
a) \(P+Q=\left(4x^2y-7xy^2-5y^3\right)+\left(x^3-6x^2y+4xy^2\right)\)
\(P+Q=4x^2y-7xy^2-5y^3+x^3-6x^2y+4xy^2\)
\(P+Q=(4x^2y-6x^2y)+\left(-7xy^2+4xy^2\right)-5y^3+x^3\)
\(P+Q=-2x^2y-3xy^2-5y^3+x^3\)
\(P-Q=\left(4x^2y-7xy^2-5y^3\right)-\left(x^3-6x^2y+4xy^2\right)\)
\(P-Q=4x^2y-7xy^2-5y^3-x^3+6x^2y-4xy^2\)
\(P-Q=\left(4x^2y+6x^2y\right)+\left(-7xy^2-4xy^2\right)-5y^2-x^3\)
\(P-Q=10x^2y-11xy^2-5y^2-x^3\)
b) \(M+N=(x^2+xy-2y+1)+\left(-x^2y^2-xy+3y\right)\)
\(M+N=x^2+xy-2y+1-x^2y^2-xy+3y\)
\(M+N=x^2+\left(xy-xy\right)+\left(-2y+3y\right)+1-x^2y^2\)
\(M+N=x^2+y+1-x^2y^2\)
\(M-N=(x^2+xy-2y+1)-\left(-x^2y^2-xy+3y\right)\)
\(M-N=x^2+xy-2y+1+x^2y^2+xy-3y\)
\(M-N=x^2+\left(xy+xy\right)+\left(-2y-3y\right)+1+x^2y^2\)
\(M-N=x^2+2xy-5y+1+x^2y^2\)
