the roots of the equation x2-7x+15=0,

题目

the roots of the equation x2-7x+15=0,
a.imaginary
b.real,rational,and equal
c.real,irration,and unequal
d.real,rational,and unequal

答案

答：
A
b^2-4ac=(-7)^2-4*15=-11<0
方程有两个共轭虚根.
A是虚根