perp distance = |Am+Bn+C| / sqrt(A^2 + B^2)
Let our line be 2x-y-1
Let our point be (x,3x^2)
distance =|2x -3x^2 -1| / rt5
distance = (3x^2 - 2x +1) / rt 5
Differentiating the numerator: 6x - 2
Thus minimum distance at x = 1/3, or when numerator = 2/3
min distance = 2/3rt5