Planar tangent condition exists when two geometric forms meet at a single point and do not intersect. This is self explanatory from figure 8.

 

Figure 8. Illustrates the existence of  planar tangent condition.

Locating tangent points on circle and arcs

The method of locating tangent points on circle and arcs as well as thhe common tangent to two circles  are shown in figure 9(a) and (b) .

Figure 9. Locating the tangent points to arcs or circles.

Drawing an arc tangent to a given point on the line
The steps  for drawing the arc tangent to a given point on a line is shown in figure 10.

1. Given line AB and tangent point T. Construct a line perpendicular to line AB and through point T.
2. Locate the center of the arc by making the radius on the perpendicular line. Put the point of the compass at the center of the arc, set the compass for the radius of the arc, and draw the arc which will be tangent to the line through the point T.

 

Figure 10. Drawing an arc tangent to the a given point on a line.