Page 121 - Numbertheory
P. 121
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n 2 − 3n + 2 = (n − 2) (n −1)
.1 n −1 n − 2
(n − 2) (n −1) = 0×1 = 0 n −2 =0 n −1=1
n −1= 2 n − 2 =1 .
. (n − 2)(n −1) = 1× 2 = 2
.( ) 3 n
n [AMC10A 2003] ( )
ed
de 10d + e
n
21 ( ) . 15 ( )
18 ( ) 17 ( )
e 10d + e e :( )
d .e ∈{3, 7}
.
.d ∈{2, 3, 5, 7}
10d + e ∈{23, 27, 33, 37, 53, 57, 73, 77}
10d + e ∈{23, 37, 53, 73} . 10d + e
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