Question 29Equilateral triangle $ABC$ has been creased and folded so that vertex $A$ now rests at $A'$ on $BC$ as shown. If $BA'=1$ and $A'C=2,$ then the length of crease $PQ$ is $\frac85$$\frac7{20}\sqrt{21}$$\frac{1+\sqrt5}{2}$$\frac{13}{8}$$\sqrt3$
