[tex]\frac{1}{x_1^2}+ \frac{1}{x_2^2}=\frac{x_2^2+x_1^2}{x_1^2x_2^2}=\frac{x_2^2+x_1^2}{(x_1x_2)^2}= \frac{\frac{b^2-2ac}{a^2}}{\left(\frac{c}{a}\right)^2}= \frac{b^2-2ac}{c^2}[/tex]
a=-1
b=10
c=10
[tex]\frac{10^2-2\cdot(-1)\cdot10}{10^2}=\frac{100+20}{100}=\frac{120}{100}=1,2[/tex]
