1995 AHSME Problems/Problem 17

Problem

Given regular pentagon $ABCDE$ , a circle can be drawn that is tangent to $\overline{DC}$ at $D$ and to $\overline{AB}$ at $A$ . The number of degrees in minor arc $AD$ is

Define major arc DA as $DA$ , and minor arc DA as $da$ . Extending DC and AB to meet at F, we see that $\angle CFB=36=\frac{DA-da}{2}$ . We now have two equations: $DA-da=72$ , and $DA+da=360$ . Solving, $DA=216$ and $da=144\Rightarrow \mathrm{(E)}$ .