CE=CA+AE=-AC+AD/2=-AC+(AB+AC)/4=AB/4-3AC/4
由题意知CE=r*AB+s*AC,所以r*AB+s*AC=AB/4-3AC/4
有(r-1/4)*AB+(s+3/4)*AC=0,AB,AC不共线,
所以r=1/4,s=-3/4,故:r+s=-1/2
CE=CA+AE=-AC+AD/2=-AC+(AB+AC)/4=AB/4-3AC/4
由题意知CE=r*AB+s*AC,所以r*AB+s*AC=AB/4-3AC/4
有(r-1/4)*AB+(s+3/4)*AC=0,AB,AC不共线,
所以r=1/4,s=-3/4,故:r+s=-1/2