-766/37
1-(21/2)-(83/37)-9.5=1-(21/2+19/2)-(83/37)=1-20-(83/37)=-19-2(9/37)=-21(9/37)负的21又37分之9，不是-21*(9/37)
-1572/74 等于-21.243243243243243.....243循环
