=(1+1000)+(2+999)+……+(500+501)
=1001+1001+……+1001
=1001×500
=5005001+2+3+4+5+6+......+1000=?那加到一千呢？不加10011+2+3+4+5+6+......+1000=(1+1000)+(2+999)+……+(500+501)=1001+1001+……+1001=1001×500=500500 1+2+3+4+5+6+......+1000+1001=(1+1000)+(2+999)+……+(500+501)+1001=1001+1001+……+1001+1001=1001×501= 501501