4-18、以下程序的功能是计算一元二次方程 的根。请在_________内填入正确内容。 float a,b,c,t,disc,twoa,term1,term2; scanf(“%f%f%f”,&a,&b,&c); if(a==0) if(___(1)___) printf(“no answer due to input error!\n”); else printf(“the single root is %f\n”,-c/b); else { disc=b*b-4*a*c; twoa=2*a; term1=-b/twoa; t=fabs(disc); term2=sqrt(t)/twoa; if(__(2)__) printf(“complex root\n real part=%f imag part=%f\n”,term1,term2); else printf(“real roots\n root1=%f root2=%f\n”,term1+term2,term1-term2); }