Question

Умоляю помогите! Решите третье задание!!!!!!!

Answer 1

$\displaystyle\bf\\x^{2} -5x-7=0\\\\Teorema \ Vieta:\\\\x_{1}+x_{2} =5\\\\x_{1} \cdot x_{2} =-7\\\\\\1)\\\\\frac{1}{x_{1} } +\frac{1}{x_{2} } =\frac{x_{1} + x_{2} }{x_{1} \cdot x_{2} } =\frac{5}{-7} =-\frac{5}{7} \\\\\\2)\\\\x_{1} ^{2} +x_{2} ^{2} =(x_{1} + x_{2} )^{2} -2x_{1} x_{2} =5^{2} -2\cdot(-7)=25+14=39$