负二分之一的2001次方+负二分之一的2000次方
=（ - 1/2）^2001 + (-1/2)^2000
= (-1/2)* (-1/2)^2000 + (-1/2)^2000
=1/2 * (-1/2)^2000
=1/2 * (1/2)^2000
=(1/2)^2001