Question: How to have labled x-Axes with multiples of π in a plot?

hey there! I was woundering.. What is the command for an ordinary plot, to lable the points on the x-Axes at points, like π, 2π, 3π and so forth. It would be very usefull for plots of trigonometric functions. I didn't find the option in the Help page. What i found, is the option by right clicking on the plot - but it is greyed out most time, and i would like to know the command anyway, so it would allways plot right, when i re-execute the Maple document. cheers!
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