# Measure of the Angle between Two Straight Lines

Measure of the Angle between Two Straight Lines

The angle between the two lines is given by .

θ=β-α

Let and be the equations of two lines in the plane, with and the slopes of the lines. The angle between them is given by

y=mx+b

1

1

y=mx+b

2

2

m

1

m

2

θ

θ=tan

-1

m-m

1

2

1+mm

1

2