Knowing that all the angles in a triangle add up to a total of 180 degrees and the relation of all angles to one another: you may plug in a value for the smallest angle and use this to calculate the other angle values, add all calculated angle measures and repeat until the value is equal to 180 degrees.
Since all angle measures in this problem are dependent upon the smallest angle measure, you only have to change the value of this variable in order to solve the problem.
Measure the distance between the two end points, and divide the result by 2. This distance from either end is the midpoint of that line. Alternatively, add the two x coordinates of the endpoints and divide by 2. Do the same for the y coordinates.
