(-1/2)×(-2)=1
（-1又1/2）×（-1又1/3）×（-1又1/4）×（-1又1/5）-(?)（-1又1/6）×(-1又1/7)
=（-3/2）×（-4/3）×（-5/4）×（-6/5）-（-7/6）×(-8/7)
= 3/2× 4/3× 5/4 × 6/5 - 7/6 × 8/7
= 6/2 - 8/6
= 3- 4/3
= 1又3分之2