Tangent lines are lines that smoothly meet an arc or circle. You can draw a line
tangent to one or two circles or arcs. For example you might need a tangent line
in designing a cam.
To draw lines tangent to one curve:
From the left toolbar enable Snap to Lines.
Draw a straight line starting away from the curve. When you approach
the tangent point, the line will snap into the tangent position.
