the discriminant of
ax^2+b+c=0 is
b^2-4ac
when the discriminant is
less than 0, then there are no real roots
equal to 0, then there is 1 real root
greater than 0, then there are 2 real roots
so
2x^2-5x+7=0
a=2
b=-5
c=7
discriminat=(-5)^2-4(2)(7)=25-28=-3
-3<0
no real roots