因为Y=根号下X-1/2+根号下1/2-X+1/2 所以要想使根号下X-1/2+根号下1/2-X有意义,则有x-1/2=0 x=1/2 y=1/2 带入5X+（2Y-1）-根号下Y*2-2Y+1 ＝5x+2y-1-(y-1) =5x+y =3
