解:(1)由題意可得 ${x}_{1}$+ ${x}_{2}$=- $\frac{a}$= $\frac{5}{2}$
${x}_{1}$× ${x}_{2}$= $\frac{c}{a}$=1
原式= ${x}_{1}{x}_{2}+{x}_{1}+{x}_{2}+1$
=1+ $\frac{5}{2}$+1
= $\frac{9}{2}$
(2)原式= $\frac{{x}_{1}2+{x}_{2}2}{{x}_{1}{x}_{2}}$
= $\frac{({x}_{1}+{x}_{2})2-2{x}_{1}{x}_{2}}{{x}_{1}{x}_{2}}$
= $\frac{25}{4}$-2
= $\frac{17}{4}$