a)\(A=\left(\frac{x+y}{x-2y}+\frac{3y}{2y-x}-3xy\right).\frac{x+1}{3xy-1}+\frac{x^2}{x+1}\)

\(=\left(\frac{x+y-3y}{x-2y}-3xy\right).\frac{x+1}{3xy-1}+\frac{x^2}{x+1}\)

\(=\left(\frac{x-2y}{x-2y}-3xy\right).\frac{x+1}{3xy-1}+\frac{x^2}{x+1}\)

\(=\left(1-3xy\right).\frac{-x-1}{1-3xy}+\frac{x^2}{x+1}\)

\(=-\left(x+1\right)+\frac{x^2}{x+1}\)`

\(=\frac{-\left(x+1\right)^2+x^2}{x+1}\)

\(=\frac{-x^2-2x-1+x^2}{x+1}\)

\(=\frac{-2x-1}{x+1}\)(1)

b) Thay \(x=-3,y=2014\)vào (1) ta được:

\(A=\frac{-2.\left(-3\right)-1}{-3+1}=\frac{-5}{2}\)

Vậy \(A=\frac{-5}{2}\)với x=-3 và y=2014

@Nguyễn Việt Lâm

câu 1 thôi 2 làm được rồi

Ta có: \(\left(2x+3y\right)\left(x^2+2y^2\right)=\left(x^2+3xy+y^2\right)\left(x+2y\right)\)

\(\Leftrightarrow2x^3+4xy^2+3x^2y+6y^3=x^3+2x^2y+3x^2y+6xy^2+x^2y+2y^3\)

\(\Leftrightarrow x^3-2xy^2-3x^2y+4y^3=0\)

\(\Leftrightarrow\left(x-y\right)\left(x^2-4xy-4y^2\right)=0\)

a: \(\frac{x+1}{x-y}+\frac{x-1}{x-y}+\frac{x+3}{x-y}\)

\(=\frac{x+1+x-1+x+3}{x-y}=\frac{3x+3}{x-y}\)

b: \(\frac{5xy^2-3z}{3xy}+\frac{4x^2y+3z}{3xy}=\frac{5xy^2-3z+4x^2y+3z}{3xy}\)

\(=\frac{5xy^2+4x^2y}{3xy}=\frac{xy\left(5y+4x\right)}{3xy}=\frac{4x+5y}{3}\)

c: \(\frac{x+9}{x^2-9}-\frac{3}{x^2+3x}\)

\(=\frac{x+9}{\left(x-3\right)\left(x+3\right)}-\frac{3}{x\left(x+3\right)}\)

\(=\frac{x\left(x+9\right)-3\left(x-3\right)}{x\left(x+3\right)\left(x-3\right)}=\frac{x^2+9x-3x+9}{x\left(x+3\right)\left(x-3\right)}\)

\(=\frac{x^2+6x+9}{x\left(x+3\right)\left(x-3\right)}=\frac{\left(x+3\right)^2}{x\left(x+3\right)\left(x-3\right)}=\frac{x+3}{x\left(x-3\right)}\)

d: \(\frac{x}{5x+5}-\frac{x-10}{10x-10}\)

\(=\frac{x}{5\left(x+1\right)}-\frac{x-10}{10\left(x-1\right)}\)

\(=\frac{2x\left(x-1\right)-\left(x-10\right)\left(x+1\right)}{10\left(x-1\right)\left(x+1\right)}=\frac{2x^2-2x-\left(x^2+x-10x-10\right)}{10\left(x-1\right)\left(x+1\right)}\)

\(=\frac{2x^2-2x-x^2+9x+10}{10\left(x-1\right)\left(x+1\right)}=\frac{x^2+7x+10}{10\left(x-1\right)\left(x+1\right)}\)

\(DK\hept{\begin{cases}x^3+2x^2y-xy^2-2y^3\ne0\\x-y\ne0\end{cases}}\)

\(\Leftrightarrow\left(x^2+3xy+2y^2\right)\left(x-y\right)=x^3+2x^2y-xy^2-2y^3\)

\(\Leftrightarrow x^3+3x^2y+2xy^2-x^2y-3xy^2-2y^3=x^3+2x^2y-xy^2-2y^3\)

\(\Leftrightarrow x^2y=0\)\(\Rightarrow ko.dung.\)

?????????

Ta phân tích mẫu:

\(x^3+2x^2y-xy^2-2y^3\)

\(=x^3+3x^2y+2xy^2-x^2y-3xy^2-2y^3\)

\(=x\left(x^2+3xy+2y^2\right)-y\left(x^2+3xy+2y^2\right)\)

\(=\left(x-y\right)\left(x^2+3xy+2y^2\right)\)

Thay vào ta có:

\(\frac{x^2+3xy+2y^2}{\left(x-y\right)\left(x^2+3xy+2y^2\right)}=\frac{1}{x-y}\)

Vậy ta có điều phải chứng minh