Find all values of $\alpha$such that the graphs of $\theta =\alpha$ and $\theta =-\alpha$ are the same in a polar coordinate system.

The equations $\theta =\alpha$ and $\theta =-\alpha .$

Consider the equations $\theta =\alpha$and $\theta =-\alpha .$

The objective is to show that $\theta =\alpha$and $\theta =-\alpha$are same in polar coordinate system.

For any real number $\alpha$, the polar equation $\theta =\alpha$describes the set of points with polar angle $\alpha$.

The angle is positive in counterclockwise direction and negative in the clockwise direction.

When $\theta =\alpha$the value of $r$can be either positive or negative.

Thus, the graph for $\theta =\alpha$is line through the pole.

When $\theta =-\alpha$the value of $r$can be either positive or negative. and $\theta =-\alpha$lies on the same line that of $\theta =\alpha$which passes through the pole.

Example:

Consider $\theta =\alpha \frac{\pi }{2}$.where $\alpha$is any integer.

The graphical representation of $\theta =\alpha$and $\theta =-\alpha$.

That means the equations $\theta =\alpha$and $\theta =-\alpha$are identical in polar coordinate system.

Therefore, the answer is $\theta =\alpha \frac{\pi }{2},\alpha$is any integer