1/2×(−1999)+(−1999)×1/3+2005×5/6.

问题描述:

1
2
×(−1999)+(−1999)×
1
3
+2005×
5
6

原式=-1999×(

1
2
+
1
3
)+2005×
5
6

=-1999×
5
6
+2005×
5
6

=(-1999+2005)×
5
6

=6×
5
6

=5.