-3/5-1/2+3/4-2/5+1/2
=-(3/5+2/5)+(1/2-1/2)+3/4
=-1+0+3/4
=-1/40-1/2-（+2/5）-（-3/4）-(+1/4) 这道题怎么写?采纳我，然后重新问