Question 200407
Draw the line.
Then imagine a small circle centered at the origin. As that circle radius grows, the circle will eventually touch the line. The point where it 'just touches' results in the drawn line being a tangent to the circle.

What do you know about the radius of a circle at a tangent point and a tangent to a circle at that point?  They are perpendicular.

What do you know about the slopes of lines that are perpendicular? They are negative inverses. 

So find the line that has a slope of -2 and contains the point (0,0).
*[invoke find_line_by_slope_and_point 0, 0, -2]
{{{y = -2x}}}

Now that you have the equations for two lines, solve them to find the point they have in common.
{{{y = (1/2)x - 2}}}
{{{y = -2x}}}
{{{-2x = (1/2)x - 2}}}
{{{-(5/2)x = -2}}}
{{{5x = 4}}}
{{{x = 4/5}}}
{{{y = -8/5}}}


Now you have two points, the origin (0,0) and the point of intersection (0.8,-1.6). Find the length between them and you have your answer.
*[invoke hummingbird_distance_2D_geo 0, 0, 0.8, -1.6]

{{{graph(400,400,-5,5,-5,5, 0.5x-2, -2x)}}}