Figure 4-35.-Circular arc tangent to a straight line andanother circular arc.CIRCULAR ARC OF AGIVEN RADIUS TANGENTTO A STRAIGHT LINE AND TOANOTHER CIRCULAR ARCThe problem in figure 4-35 is to draw acircular arc with a radius equal to AB, tangentto the circular arc CD and to the straight line EF.Set a compass to a radius equal to the radius ofthe circular arc CD plus the given radius AB(which is indicated by the dashed line shown),and, with O as a center, strike the arc GH. Drawa line IJ parallel to EF at a distance from EF equalto AB. The point of intersection (P) between GHand IJ is the center of the circle of which an arcof the given radius is tangent to CD and EF.CIRCULAR ARC OF A GIVENRADIUS TANGENT TO TWOOTHER CIRCULAR ARCSThe problem in figure 4-36 is to draw an arcwith a radius equal to AB, tangent to the circulararcs CD and EF. Set a compass to a spread equalto the radius of arc CD plus AB (indicated by theleft-hand dashed line), and, with O as a center,strike an arc. Set the compass to a spread equalto the radius of arc EF plus AB (indicated by theright-hand dashed line), and, with O´ as a center,strike an intersecting arc. The point of inter-section between the two arcs (P) is the center ofthe circle of which an arc of given radius is tangentto arcs CD and EF.In figure 4-36 the circular arcs CD and EFcurve in opposite directions. In figure 4-37 theproblem is to draw an arc with radius equal toAB, tangent to two circular arcs, CD and EF, thatcurve in the same direction.Set a compass to a radius equal to the radiusof EF less AB, and, with O´ as a center, strikean arc. Then, set a compass to a radius equal tothe radius of arc CD plus line AB, and, with Oas center, strike an intersecting arc at P. The pointof intersection of these two arcs is the center ofthe circle of which an arc of the given radius istangent to CD and EF.When a circular arc is tangent to another, itis commonly the case that the two arcs curve inopposite directions. However, an arc may bedrawn tangent to another with both curving in thesame direction. In a case of this kind, the tangentarc is said to enclose the other.Figure 4-36.-Circular arc tangent to two other circulararcs.Figure 4-37.-Circular arc tangent to arcs that curve in thesame direction.4-12