x²+x-3=0
x1是方程的根
所以x1²+x1-3=0
x1²=-x1+3
x1³=x1×x1²
=x1(-x1+3)
=-x1²+3x1
=-(-x1+3)+3x1
=4x1-3
同理
x2²+x2-3=0
x2²=-x2+3
由韦达定理,x1+x2=-1
原式=(4x1-3)-4(-x2+3)+19
=4(x1+x2)-3-12+19
=4×(-1)+4
=0