x+1分之1-1-x)除以x 的平方-1分之1=（1-（x+1）²）/(x+1)×(x+1)(x-1)=(-x²-2x)(x-1)=-x(x-1)(x+2)=-1/2×(1/2-1)×(1/2+2)=-1/2×(-1/2)×(5/2)=5/8;
