__Inclination of a Line__**:**

Angle from X-axis to any given non horizontal line is called inclination of line . Here is the inclination where , measured in the counter clockwise direction from the positive X-axis to the line .

__Slope of a Line__**:**

If is the inclination of a non-vertical straight line , then its slope or gradient is defined as . The slope of a straight line is usually denoted by , so formula to find the slope of a line is given by

If a straight line is parallel to X-axis, then its slope is equal to zero i.e. . If the straight line is parallel to Y-axis, then its slope is undefined i.e. .

If the line is parallel to X-axis, then ordinate of each point on the line is a fixed number, so its equation will be , where is some fixed number. If the line is parallel to Y-axis, then abscissa of each point on the line is a fixed number, so its equation will be , where is some fixed number.

Let be the slopes of the lines respectively.

**(i)**The lines and are parallel if and only if

**(ii)**The lines and are perpendicular if and only if

__Example__**:** Find the slope of straight line with inclination with X-axis.

Here we have the inclination with X-axis, now shall find the slope of straight line using the formula ,