ax^2+bx+c=0, c=g, a=1, b=5
x1^2+x2^2=7, (x1+x2)^2 - 2*x1x2=7, ()^2-2( , ()^2-2* =7, 25-2g=7, 2g=18, g=9
ax^2+bx+c=0, c=g, a=1, b=5
x1^2+x2^2=7, (x1+x2)^2 - 2*x1x2=7, ()^2-2( , ()^2-2* =7, 25-2g=7, 2g=18, g=9