[填空题]
Two concentric circles wid5xdrw 4dcy1e1bsc /4th centre O are shown4br bf9wko f w7m1pjcaeb1m:/ o7h:l3 in the diagram below. The radius of the smaller circle is 5 cm and the radius of the larger cifh9wbombac 7:/w r3p:4o11 lj fmkbe7rcle is 7 cm. Points A and B lie on the circumference of the larger circle such that angle $\mathrm{A}\hat{\mathrm{O}}\mathrm{B}$ is $\frac {\pi}{5}$ radians.
1.Find the length of the short arc AB. cm
2.Find the area of the shaded region. $cm^2$
