Here is a quick tip on drawing tangent lines and arcs. Before getting started, you can easily drawing tangent arc and line segments when using POLYLINEs, but we are going to discuss using plain LINE and ARC entities.
Let’s say you draw a line, and now you want to draw an arc from the endpoint, tangent to the line. Start the ARC command, but when you are prompted for a start point, press ENTER. The last point will be used as the start point and then you are prompted to pick the second endpoint of the arc. The resulting arc will be tangent to the line. Notice the black line, and then the red arc being drawn.
The same thing applies if you are going the other way. Draw an arc, then start the LINE command. Instead of picking a point, just press ENTER. Now your are prompted to pick the second endpoint of the line, except that the line is constrained to be tangent to the arc. Below….notice the arc in black, then the line being constructed in red.