Re: [請益] 國中數學問題
※ 引述《begin530 (藍風)》之銘言:
: 「將-6,-4,-2,0,2,4,6,8,10共9個整數,填入九宮格中,
: a 10 b
: 6 X
: c 8
: [(-6)+(-4)+(-2)+0+2+4+6+8+10]/9=2
: 即 X = 2 .......這步我不大懂,why?
(1) (2) (3)
(4) (5) (6)
(7) (8) (9)
X的求解利用國二等差中項的觀念 a,b,c成等差 => a+c=2b ,a+b+c=3b
(1)+(2)+(3) = 3 * (2) ..... 1 式
(4)+(5)+(6) = 3 * (5) ..... 2 式
(7)+(8)+(9) = 3 * (8) ..... 3 式
1 式 + 2 式 + 3 式
=> (1)+(2)+(3)+(4)+(5)+(6)+(7)+(8)+(9)= 3 * (2) + 3 * (5) + 3 * (8)
= 3 * [ (2) + (5) + (8) ]
= 3 * 3 * (5)
= 9 * (5) = 9 * X
所以 X = [(-6)+(-4)+(-2)+0+2+4+6+8+10] / 9 = 2
參考看看
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