指數記數法(f.3)

方法一：利用指數定律 3^a / 3^b = 3^(a - b)

3^(2n+1) / 3^(2n-1)

= 3^[(2n + 1) - (2n - 1)]

= 3^(2n + 1 - 2n + 1)

= 3^2

= 9


= = = = =
方法二：在分子和分母以公因式表示（這題是 2^2n），然後約去公因式得答案。

3^(2n+1) / 3^(2n-1)

= (3^2n x 3^1) / (3^2n x 3^-1)

= (3^1) / (3^-1)

= 3 / (1/3)

= 3 x 3

= 9

2011-01-17 19:47:51 補充：
方法二所用的指數定律是：3^(a + b) = 3^a x 3^b

2011-01-17 22:16:33 補充：
(3x3^n+1-6x3^n-1) / 5x3^n-1
= (3x3^[2+(n-1)]-6x3^n-1) / 5x3^n-1
= (3x3^2x3^(n-1)-6x3^n-1) / 5x3^n-1
= (27x3^(n-1)-6x3^n-1) / 5x3^n-1
= 3^(n-1)(27 - 6) / 5x3^n-1
= 21/5 ..... 答案

將佢地爆曬先..

3X3^nX3-6X3^nX3^-1
5X3^nX3^-1

抽3^n次方

3^n(9-2)
3^n(3份之5)

約曬3^n.除變乘..

7X3份5
=21份之5

3^2n+1
—
3^2n-1
_____________
3^2n+1-(2n-1)
3^2n+1-2n+1
3^2 or 9