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mathtrigonometryalgebrapi

Getting theta of Line Equation

Please forgive my lack of knowledge, which i think it's one of those basic formula related to Trigonometry.

Let's look at visual example: enter image description here

I have 5 lines, with their line equation (let's say they have zero offset ok)
how can i calculate the Theta of each line equation make (in Pi)?

also I have seen this: enter image description here

Are they generated from Theta of line equations? or it's another theory which help to find the theta?
much appreciate your time and effort

Solution

  • For equation

    y = k * x

tg(Theta) = k

    and

    Theta = Arctg(k) //arctangent function

    General line equation 

    A * x + B * y + C = 0

    (It is more general than y=ax+b and includes cases of vertical and horizontal lines)

    Theta = atan2(A, B)

    (function atan2 or ArcTan2 exists in math libraries of many programming languages)