請高手指點一條數

Method 1

this is very simple to evaluate for this question

(a) 18n + 12 = 6 (3n + 2) >>> factor of 6

(b) 3(2n - 1 ) +1 = 6n - 3 + 1 = 6n - 2 = 2 (3n-1) >>>>> factor of 2

Method 2

using M.I.

a18N+12=6(6N+2) so18N+12是6的倍數。

b首先2N必定是偶數,-1後是單數,X3後又是單數,+1後是偶數...



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