Equate the two functions to get x^2 = m*x - 2 or x^2 - m*x + 2 = 0
This quadratic has a single point solution if (-m)^2 - 4*1*2 = 0 or m^2 = 8
Therefore there are two possibilities: m = sqrt(8) and m = -sqrt(8)
These mean that the linear function represents tangent lines to the x^2 function.