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- 蒼穹之秋Lv 61 0 年前最佳解答
18的因數有︰1、2、3、6、9、18
因為 (a,b) ×〔a,b〕 = a × b
則 (x,18) × 〔x,18〕 = x × 18
若 (x,18) = 1 ............. 則 1 × 90 = 18x .......... x = 5
若 (x,18) = 2 .................... 2 × 90 = 18x ............ x = 10
若 (x,18) = 3 ..................... 3 × 90 = 18x .............. x = 15
若 (x,18) = 6 ...................... 6 × 90 = 18x .................x = 30
若 (x,18) = 9 ...................... 9 × 90 = 18x .................. x = 45
若 (x,18) = 18 ................... 18 × 90 = 18x .................. x = 90
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