You can use the Tangent 
constraint to create a tangent relationship between sketch elements. A line is tangent to a curve and perpendicular to the radius when it touches it at exactly one point. A line that is tangent to an arc (or circle) will be perpendicular to the arc's radius. Arcs and circles can also be tangent to each other. When curves are tangent to each other, they touch at exactly one point.
To create a Tangent constraint:
- Select two sketch elements, either a line and a curve, or two curves.
- From the constraints menu, select Tangent.
Tangent elements do not need to be in contact with each other. When tangent elements are separated, guide curves are shown to indicate where the tangency applies.
Learn more by watching the video below:
