Help needed defining and graphing a straight line function!

In working on a project I need to define a line that runs through the origin(Y-intercept = (0,0)), and the gradient is based off of an input angle. If I want the angle between the line and the X-axis to be within a range of 90 to -90 degrees and the only input variable is an angle, how would I define the equation of this line?

If any further information is needed please let me know, many thanks in advance and apologies for the poor wording, wasn't quite sure how to ask what I'm looking for!