设a=c+di,c、d均为实数,x为实数.代入方程得：x^2+cx+(dx+4)i=0,∴x^2+cx=0,dx+4=0,∴c=-x,d=-4/x.∴|a|^2=c^2+d^2=x^2+16/x^2≥2√16=8,又x^2=1时,x^2+16/x^2=17,x^2=16时,x^2+16/x^2=17,∴|a|的最大值√17,最小值2...