By Notes Vandar
Equation of straight line in slope intercepts form:
Let P(x, y) be the any point line AB which makes a positive angle θ with x-axis.
∠ ACD= ∠ABE = θ
Slope of line AB = tanθ = m
PD = y- c
CD = OE =x
Angle betweenlines y = m1x+ c2andy =m2 x+ c1