This image was acquired from
wikimedia. It was marked as Public Domain or CC0 and is free to use. To verify, go to the source and check the information there.
Keywords from Image Description:
Unitcircledefs.svg Characterization of the sine tangent and secant functions using certain vertical lines SVG redraw from original work Unitcircledefs svg UTC Unitcircledefs svg en User Michael Hardy original Pbroks talk redraw derivative work Vancho talk Added coloring changed name tan to tg added angle name theta italicized