例1:计算:
19+199+1999+19999+199999
解:
=20+200+2000+20000+200000-15=222220-5
=222215
例2:1^2+2^2+3^2+4^2++10^2
运用公式:1^2+2^2+3^2++N^2=N(N+1)(2N+1)6
解:1^2+2^2+3^2+10^2
=10(10+1)(210+1)6
=1011216
=385