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2006-10-26 16:59:14 · 4 個解答 · 發問者 ? 1 in 科學 ➔ 數學
3(3^x)-3^(x-1)=216
3(3^x)-(3^x)(3^-1)=216
(3^x)(3-1/3)=216
3^x(8/3)=216
3^x=216*3/8
3^x=81
x=4
2006-10-26 17:03:50 · answer #1 · answered by Amby 6 · 0⤊ 0⤋
3(3^x)-3^(x-1)=216
3(3^x)-(3^x)(3^-1)=216
(3^x)(3-1/3)=216
3^x=216*3/8
3^x=81
x=4
2006-10-26 17:06:25 · answer #2 · answered by ? 3 · 0⤊ 0⤋
可唔可以 copy 出埋來睇吓?
2006-10-26 17:05:08 · answer #3 · answered by 唔眼訓 3 · 0⤊ 0⤋
3 (3 ^ x) - 3 ^(x - 1) = 216
3 ^ (x + 1) - 3 ^ (x - 1) = 216
3^ x ( 3 - (1 / 3)) = 216
3^ x (8 / 3) = 216
3^ x = 81
3^ x = 3^ 4
x = 4
2006-10-26 17:04:10 · answer #4 · answered by J 7 · 0⤊ 0⤋