[tex]\displaystyle\bf\\x^{2} -8x+11=0\\\\Teorema \ Vieta \ :\\\\x_{1} + x_{2} =8\\\\x_{1} \cdot x_{2} =11\\\\\\\frac{1}{x_{1} }+\frac{1}{x_{2} }=\frac{x_{1} + x_{2}}{x_{1} \cdot x_{2} } =\frac{8}{11} \\\\\\Otvet \ : \ \frac{1}{x_{1} }+\frac{1}{x_{2} }=\frac{8}{11}[/tex]