We can clearly see a line ‘a’ whose equation is y=mx +c. We can change the values of m (slope of this line) and (x1, y1), the co-ordinates of the given point A through which this line passes using their corresponding slide bars. Observe how the position of this line changes as we change the values of m, x1 and y1

Questions to think about
Angle α between the line and the positive x-axis is given. Calculate tanα, what do we observe? Hint, compare tanα with m.
Fix the values of x1 and y1 and change the value of m, what do we observe?
Fix the value of m and change the value of x1 and y1 using their corresponding slide bars or by directly moving the point A, what do we observe?
Input values of x1 and y1 in the equation y-y1=m(x-x1) and compare the result with equation of line ‘a’ which we see in the screen