On the Tools menu click Snaps to select Tangent To when the command prompt requests a point to use this modifier.
TANGENT TO selects a point on a circle, arc, ellipse, spline, or smooth polygon that forms a tangent from the last point selected. You can use TANGENT TO whenever CC3 prompts you for a point. Usually you will place at least one point before selecting TANGENT TO. The prompt reads "Tangent to:". Select an entity. CC3 draws the line or line segment tangent to that entity.
Text equivalent: TAN