Χ1和Χ2是方程aΧ²+bΧ+c=0（a≠0）的解
所以X1+X2=-b/a,X1*X2=c/a
Χ1²+Χ2²=(X1+X2)^2-2X1X2=b^2/a^2+2bc/a^2=(b^2+2bc)/a^2=(b+2c)b^2/a^2
Χ1³+Χ2³=(X1+X2)(X1^2-X1X2+X2^2)=-b/a*[(b^2+2bc)/a^2-c/a]=bc/a^2-(b+2c)b^2/a^3
Χ1+Χ2=-b/a
a（Χ1³+Χ2³）+b（Χ1²+Χ2²）+c（Χ1+Χ2）=bc/a-(b+2c)b^2/a^2+(b+2c)b^2/a^2-b/a=b(c-1)/a