如果一元二次方程ax2+bx+c=0(a≠0)的两个根是x1,x2,那么x1+x2=-ba;x1x2=ca.这就是著名的韦达定理.根据韦达定理,可得出以下两个推论.推论1设x1,x2是一元二次方程ax2+bx+c=0(a≠0)的两根,则x1-x2=Δ姨a,其中Δ=b2-4ac.利用韦达定理很容易证明推论1.推论2如果一元二次方程ax2+bx If the two roots of the quadratic equation ax2+bx+c=0 (a≠0) are x1,x2, then x1+x2=-ba;x1x2=ca. This is the well-known Weida theorem. The following two corollaries can be derived. Corollary 1 Let x1 be the two quadratic equations where ax2+bx+c=0 (a≠0). Then x1-x2=Δ姨a, where Δ=b2- 4ac. It is easy to prove the inference by using the Weddah’s theorem. 1. Inference 2 If the unitary quadratic equation ax2+bx