Find the positive constant k so that the equation 3sqrt(x) = x+ k has a unique solution in x.
3sqrt(x) = x + k
Squaring both sides: 9x = x2 + 2xk + k2
Rewriting: x2 - 9x + 2kx + k2 = 0
x2 + (2k - 9)x + k2 = 0
This is a quadratic; it will have a unique solution when the discriminant of the quadratic formula is zero.
For the quadratic formula: a = 1 b = 2k - 9 c = k2
Discriminant: b2 - 4·a·c = 0
(2k - 9)2 - 4·(1)·(k2) = 0
4k2 - 36k + 81 - 4k2 = 0
-36k + 81 = 0
-36k = -81
k = 9/4