$\"\"$

$\"\"$ = the angle between the positive $\"\"$ - axis and a non-horizontal, non-vertical line $\"\"$ (or) inclination of line $\"\"$ .

Let

$\"\"$ Slope of line $\"\"$ .

FInd the slope of line $\"\"$ .

Since the lines $\"\"$ and $\"\"$ are parallel, slopes of the lines is equal.

$\"\"$

The line $\"\"$ is passing through the origin and it touches the unit circle at point $\"\"$ .

$\"\"$ ( since radius of unit circle is 1 )

Slope formula of line $\"\"$ .

$\"\"$

Substitute $\"\"$ .

$\"\"$

$\"\"$ . (since $\"\"$ )

$\"\"$

The slope of a non - horizontal, non - vertical line $\"\"$ is $\"\"$ .