GC=GE+EC设DG=x*DE=x*(DC+CE)=x*a-1/2*x*bAG=y*AF=y*(AD+DF)=1/2*y*a+y*bAG-DG=AD=(1/2*y-x)*a+(1/2*x+y)*b=b{1/2*y-x=0{1/2*x+y=1解得{x=2/5{y=4/5DE=3/5*DE=3/5*(a-1/2*b)=3/5*a-3/10*bDC=DE+EC=3/5*a-3/10*b+1/2*b=3/5*a+1/5*b