19+199+1999.+19个9=

问题描述:

19+199+1999.+19个9=

9个919+199+1999+……+1999999999=19+1+199+1+1999+1+……+1999999999+1-9×1=20+200+2000+……+2000000000-9=2222222220-9=222222221119个919+199+1999+……+199……………9=19+1+19...