Using the discriminant to determine the number of roots

The discriminant is the part of the quadratic formula underneath the square root symbol: b^2−4ac. The discriminant tells us whether there are two solutions, one solution, or no solutions.

If b^2−4ac=0 (1 real root)
If b^2−4ac greater than 0 (2 real root)
If b^2−4ac less than 0 (0 real root)

Q. Determine the number of roots for each quadratic function.

a) x^2−10x+25=0

b) 3x^2−75=0

c) 4x^2−10x=−25

d) x^2+4x+20=0

e) 4x^2−36=0

f) 9x^2−12x=−4

[RankInfinium]

a question if you dont mind, how can there be only 1 real root in a quadratic? arent imaginary always in pair?