The angle between the lines 2x – y + 3 = 0 and x + 2y + 3 = 0 is
Let m1 and m2 be the slope of the lines 2x − y + 3 = 0 and x + 2y + 3 = 0, respectively.
Let θ be the angle between them.
Here, m1 = 2 and m2
∵ m1m2 = − 1
Therefore, the angle between the given lines is 90°.