distance along a line
Find The Location Of A Point, (x,y),
On A Given Line, y = m x + b,
At A Given Distance, d,
Starting From A Given Point, (x1,y1)
The answer should be expressed in terms of known information: d, x1, y1, m or b.

x =

y =

Hint: Start with the distance formula

d = ((x - x1)^2 + (y - y1)^2)^.5

The Point Plotting Theorem Of Geometry
    Constructing a point on a line at a given distsnce from a given point on the line with a compass is an important drawing exercise.
After you find a formula for x in terms of x1, m and d use m = tan A to write a corresponding formula for x in terms of x1, cos A and d.

After you find a formula for y in terms of y1, m and d use m = tan A to write a corresponding formula for y in terms of y1, sin A and d.

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