По теореме Виета
x_(1)+x_(2)=-p
x_(1)*x_(2)=-15
[m]\frac{x_{1}}{x_{2}}+\frac{x_{2}}{x_{1}}=\frac{x^2_{1}+x^2_{2}}{x_{1}\cdot x_{2}}=\frac{(x_{1}+x_{2})^2-2x_{1}\cdot x_{2}}{x_{1}\cdot x_{2}}=\frac{(-p)^2-2\cdot(-15)}{(-15)}=-\frac{p^2+30}{15}[/m]