Angle Between Two Lines Calculator

A calculator to find the angle between two lines L1 and L2 given by their general equation of the form

a x + b y = c

The formula used to find the acute angle (between 0 and 90) between two lines L1 and L2 with slopes m1 and m2 is given by

θ = |tan -1( (m2 - m1) / (1 + m2 m1))|

where the slopes m1 and m2 are given by - b / a for each line.
The obtuse angle α between the same lines is given by

α = 180 - θ

1 - Use Angle Between two Lines Calculator

Enter the coefficients a,b and c as defined above for lines L1 and L2 as positive real numbers and press "Calculate The Angles". The outputs are the acute and obtuse angles, in DEGREES, between the two lines.

Line L1
a = , b = , c =
Line L2
a = , b = , c =
Decimal Places =
θ =
α =

More References and Links

General Equation of a Line: ax + by = c.
Equations of Lines in Different Forms.
Online Geometry Calculators and Solvers.

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