r=60 a=135度=135/180*pai=27/36pai=3/4pai
弦长^2=r^2+r^2-2r^2cos(3/4pai)=2r^2(1-cos3/4pai)=2r^2(1+cospai/4)=2r^2(1+根号2/2)
=2*60^2(1+根号2/2)
=60^2(2+根号2)
弦长=60根号(2+根号2)=110.8655