"-2"-2<=a<=2"是“实系数一元二次方程x^2+ax+z=0有虚根”的什么条件?
"-2x^2+ax+z=0有虚根即是判别式b^2-4ac<0a^2-4z<04z>a^2因为"-2<=a<=2",所以a^2<=44z>4z>1