3/2 x 5/7 - (-5/7)x5/2 +(-1/2) 除以7/5
=3/2*5/7+5/7*5/2-1/2*5/7
=5/7*（3/2+5/2-1/2）
=5/7*7/2
=5/2
=2又2分之1