Page 70 - Numbertheory

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13 :( )

4 .3
11100
. 00

.1+1+1+ 0+ 0 = 3

21999 × 52001 [AHSME 1999] ( )

7( ) 5( ) 4( ) 2 ()

.1999 :( )

21999 × 52001 = 21999 × 51999 × 52 = 25×101999
25000 ... 000

. 2+5=7

k = 20082 + 22008 [AMC10A 2008] ( )

6( ) k 2 + 2k

8( ) 4( ) 2 ()

. 4 82 = 64 20082 :( )

4 2

2, 4, 8, 6, 2, ...

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