mx^2+12x+9m=0. for what values of m will the equation have one repeated root?

Question

I can't remember how to calculate double root values

Answer 1

quadratic have double, or equal roots when the discriminant is zero
i.e.
b^2 - 4ac = 0

12^2 - 4m(9m) = 0
144 = 36m^2
m^2 = 4
m = ± 2