因为x-1/2>=01/2-x>=0所以x=1/2从而y=1/2所以5x+|2y-1|-根号下y²-2y+1=5×1/2+0-|1/2-1|=5/2-(1-1/2)=2
求5x+|2y-1|-根号下y²-2y+1=5X-1+2Y-|Y-1|再把y=（根号下x-1/2）+（根号下1/2-x）+1/2，代入可消去未知数
