负七分之五3/7-(9/14+1/2)=3/7-(9/14+7/14)=6/14-16/14=-10/14=-5/7
七分之三减(十四分之九加二分之一)等于几？-0.714285714286
3/7 I（9/14-1/2）II 6/14 I（9.14-7/14）II 6.14-2/14 II 4/14 II 2/7
3/7 - （9/14 + 1/2）6/14 - (9/14 + 7/14) = - (10/14) = - (5/7)
