I found it very insightful to think of this in terms of the alternate dot product equation: V⋅N=∥V∥∥N∥cos(θ).
The magnitude doesn't matter since we only care about the sign.
If the cosine's angle is in [0, 90) then the x-position is positive as we are in Q1.
If the cosine's angle is 90 then the x-position 0.
If the cosine's angle is [90, 180) then the x-position is negative as we are in Q3.
Note that we cannot be greater or equal than 180 for any one degree in the triangle per the triangle inequality/definition of a triangle (has 180 degrees total).
I found it very insightful to think of this in terms of the alternate dot product equation: V⋅N=∥V∥∥N∥cos(θ).
The magnitude doesn't matter since we only care about the sign.
Note that we cannot be greater or equal than 180 for any one degree in the triangle per the triangle inequality/definition of a triangle (has 180 degrees total).