Question

1+2-3+4-5+...-4999+5000=

Answer 1

1-2+3-4+5-6+7-8+.+4999-5000

=(1-2)+(3-4)+(5-6)+(7-8)+...+(4999-5000) 每个括号里和为-1,共2500个括号

=（-1）*2500

=-2500