{ printf("输入错误，不能构成等式！\n");} } else { printf("只能构成一元一次方程，x=%.2lf\n",0==-(double)c/b ? 0 : -(double)c/b);} } else { d=b*b-4*a*c;if(d<0){ printf("x1=%.2lf+%.2lfi\nx2=%.2lf-%.2lfi\n",(-b)/(2.0*a),sqrt(-d)/(2....