Given:

The equations of the lines are

3x + y + 12 = 0 … (1)

x + 2y − 1 = 0 … (2)

To find:

Angles between two lines.

Explanation:

Let m₁ and m₂ be the slopes of these lines.

m₁ = -3, m₂

Let θ be the angle between the lines.
Then,

⇒

Hence, the acute angle between the lines is 45°