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标题: 3^90+4^90的个位数字 [打印本页]

作者: francoiswang 时间: 2012-4-19 07:10 标题: 3^90+4^90的个位数字

话说我知道看循坏数字,3 是四次一循环,4是两次.但是如何知道如何定位到具体数字呢?　例如９０／４＝２２．５　应该看　３　，９，７　，１呢　请达人详细教我如何循环地位，谢谢了

作者: Flnforever 时间: 2012-4-19 20:51

3^1 look at 3, 3^2 look at 9, 3^3 look at 7 (27), 3^4 look at 1

(81), 3^5 look at 3 (243) back to 3 again....repeat every 4 number

90=88+2=4*22+2...so u only need to look at 2 - which means 9 is the

unit number.

for 4^90, the unit number is alternating between 4 and 6, repeating

every 2 number, so for 90 you get 6.

9+6=15..unit number is 5..

i think this is correct...hope it helps..LOL

作者: 天叉包子 时间: 2012-4-20 06:48

把3四次方变成81，把4平方变成16，easier

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