По теореме Виета
х1+х2=-18, х1*х2=-8
(х1+х2)^2=(-18)^2
x1^2+2*x1*x2+x2^2=324
x1^2+x2^2=324-2*x1*x2
x1^2+x2^2=324-2*(-8)
x1^2+x2^2=324+16
x1^2+x2^2=340
По теореме Виета
х1+х2=-18, х1*х2=-8
(х1+х2)^2=(-18)^2
x1^2+2*x1*x2+x2^2=324
x1^2+x2^2=324-2*x1*x2
x1^2+x2^2=324-2*(-8)
x1^2+x2^2=324+16
x1^2+x2^2=340