y=\frac{20}{x}\\ b)\frac{5x}{10}-\frac{80}{x}=-18\\ \frac{5x^2}{10x}-\frac{800}{10x}=-18\\ \frac{5x^2-800}{10x}=-18\\ 5x^2-800+180x=0\\ x^2+36x-160=0\\ D=1296+640=1936\\ x_{1}=\frac{-36+44}{2} \ x_{1}=4\\ x_{2}=\frac{-36-44}{2} \ x_{2}=-40\\ y_{1}=5\\ y_{2}=\frac{1}{2}\\" alt="\left \{ {{0,5x-4y=-18} \atop {yx=20}} \right.\\ a)yx=20 =>y=\frac{20}{x}\\ b)\frac{5x}{10}-\frac{80}{x}=-18\\ \frac{5x^2}{10x}-\frac{800}{10x}=-18\\ \frac{5x^2-800}{10x}=-18\\ 5x^2-800+180x=0\\ x^2+36x-160=0\\ D=1296+640=1936\\ x_{1}=\frac{-36+44}{2} \ x_{1}=4\\ x_{2}=\frac{-36-44}{2} \ x_{2}=-40\\ y_{1}=5\\ y_{2}=\frac{1}{2}\\" align="absmiddle" class="latex-formula">