y'=z+xz'\\ z+xz'=\dfrac{1+2z}{2-z}\\ xz'=\dfrac{1+2z-2z+z^2}{2-z}\\ xz'=\dfrac{1+z^2}{2-z}\\ \int \dfrac{2-z}{1+z^2}dz=\int\dfrac{dx}{x}\\ (*)\int \dfrac{2-z}{1+z^2}dz=2\int \dfrac{1}{1+z^2}dz-\dfrac{1}{2}\int \dfrac{2z}{1+z^2}dz= 2arctgz-\dfrac{1}{2}ln(z^2+1)+C\\ 2arctgz-\dfrac{1}{2}ln(z^2+1)+C=lnx\\ 2arctg\dfrac{y}{x}-\dfrac{1}{2}ln(\dfrac{y^2}{x^2}+1)+C=lnx" alt="y=xz=>y'=z+xz'\\ z+xz'=\dfrac{1+2z}{2-z}\\ xz'=\dfrac{1+2z-2z+z^2}{2-z}\\ xz'=\dfrac{1+z^2}{2-z}\\ \int \dfrac{2-z}{1+z^2}dz=\int\dfrac{dx}{x}\\ (*)\int \dfrac{2-z}{1+z^2}dz=2\int \dfrac{1}{1+z^2}dz-\dfrac{1}{2}\int \dfrac{2z}{1+z^2}dz= 2arctgz-\dfrac{1}{2}ln(z^2+1)+C\\ 2arctgz-\dfrac{1}{2}ln(z^2+1)+C=lnx\\ 2arctg\dfrac{y}{x}-\dfrac{1}{2}ln(\dfrac{y^2}{x^2}+1)+C=lnx" align="absmiddle" class="latex-formula">