Find the obtuse angle between the following pair of straight lines.

Given:

To find:

The obtuse angle between the given pair of straight lines.

Solution:

The slope intercept form of a line is

    ...(i)

where, m is slope and b is y-intercept.

The given equations are

On comparing these equations with (i), we get

Angle between two lines whose slopes are is

Putting and , we get

Now,

and

and

and

, so it is an obtuse angle and , so it is an acute angle.

Therefore, the obtuse angle between the given pair of straight lines is 120°.

use this formula:

p(a\b) = p(a and b)/p(b).

take it from here.