For two real values of n, the equation 9x^2+nx+36=0 has exactly one solution in x. What is the positive value of n?

 9x^2+nx+36=0

If this has only one [ double root ] solution......the discriminant will = 0

So

n^2  - 4(9)(36) =  0

n^2 - 36^2  = 0

n^2  = 36^2

n = 36