由 chanjunhong 於 星期四 八月 04, 2005 4:59 pm
7x97=79 (mod 100)
17x87=79 (mod 100)
...47x57=79 (mod 100)
79^5=99 (mod 100)
7x17x27x.....1967=99^(19)x7x17x27X37X47X57X67 (mod 100)
=67 (mod 100)
更正:求7*31*55*...........*(24n-17)*............*2887的末兩位為?
x=120Xk+55
y=24
(x-2y)(x-y)x(x+y)(x+2y)=x^5-5y^2x^3+4y^4x (mode 100)
x=25 (mod 100) ; 5y^2x^3=0 (mod 100)
4y^4x= 20, 0, 80, 60 40 (mode 100)
自行驗證 任意總和mod 100 為 25
25X87=75 (mod 100)
我覺得我方法太笨了,有更好的方法嗎?