Mathematics
Senior High
整数問題です。赤線の部分が分かりません…なぜ急に2が出てきたのでしょうか。
教えてください🙏🙇♀️
2 [2019 信州大]
(1) 2-1が3で割り切れるような自然数n をすべて求めよ。
(2) n-1が3で割り切れるような自然数n をすべて求めよ。
(1) (1)
n=19&z=1
n=299€=3
n=3のとも =7
h = 4art = 15
$₂11=2 marz
こ
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(1) 自然数nをu=2m, 2m-l(自然数人とおしく、
(il n = 2m98z
2"-1=22m - 1 = 4m - 1
ここで4=11mod31より
24- | = 4m_1 = 1 m² | = 1-1=0 ( mod3)
(iil n = 2m-1982
24-1 = 22m² 1 | = 2.2² (m-111
2-1 = 2.2
2(m-1/
- 1 = 2.4" = 1 = 2.1 M-1-1
= | (mod 3)
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