第32页

信息发布者:
解:
菱形的边长为:
$\begin{aligned}&\sqrt{(\frac{2\sqrt{3}+2}{2})^2+(\frac{2\sqrt{3}-2}{2})^2}\\=&\sqrt{(\sqrt{3}+1)^2+(\sqrt{3}-1)^2}\\=&\sqrt{3+2\sqrt{3}+1+3-2\sqrt{3}+1}\\=&\sqrt{8}\\=&2\sqrt{2}\end{aligned}$
周长为:$4×2\sqrt{2}=8\sqrt{2},$
面积为:$\frac{1}{2}×(2\sqrt{3}+2)×(2\sqrt{3}-2)=\frac{1}{2}×[(2\sqrt{3})^2-2^2]=\frac{1}{2}×(12-4)=4$
答:菱形$ABCD$的周长为$8\sqrt{2},$面积为4。
(1) 解:
当$n=1$时,
$\begin{aligned}&\frac{1}{\sqrt{5}}[(\frac{1+\sqrt{5}}{2})^1-(\frac{1-\sqrt{5}}{2})^1]\\=&\frac{1}{\sqrt{5}}×\frac{1+\sqrt{5}-1+\sqrt{5}}{2}\\=&\frac{1}{\sqrt{5}}×\sqrt{5}\\=&1\end{aligned}$
当$n=2$时,
$\begin{aligned}&\frac{1}{\sqrt{5}}[(\frac{1+\sqrt{5}}{2})^2-(\frac{1-\sqrt{5}}{2})^2]\\=&\frac{1}{\sqrt{5}}×(\frac{1+\sqrt{5}}{2}+\frac{1-\sqrt{5}}{2})×(\frac{1+\sqrt{5}}{2}-\frac{1-\sqrt{5}}{2})\\=&\frac{1}{\sqrt{5}}×1×\sqrt{5}\\=&1\end{aligned}$
所以第1个数和第2个数均为1。
(2) 证明:
$\begin{aligned}x_{n+1}-x_n&=\frac{1}{\sqrt{5}}[(\frac{1+\sqrt{5}}{2})^{n+1}-(\frac{1-\sqrt{5}}{2})^{n+1}]-\frac{1}{\sqrt{5}}[(\frac{1+\sqrt{5}}{2})^n-(\frac{1-\sqrt{5}}{2})^n]\\&=\frac{1}{\sqrt{5}}[(\frac{1+\sqrt{5}}{2})^{n+1}-(\frac{1+\sqrt{5}}{2})^n-(\frac{1-\sqrt{5}}{2})^{n+1}+(\frac{1-\sqrt{5}}{2})^n]\\&=\frac{1}{\sqrt{5}}[(\frac{1+\sqrt{5}}{2})^n(\frac{1+\sqrt{5}}{2}-1)-(\frac{1-\sqrt{5}}{2})^n(\frac{1-\sqrt{5}}{2}-1)]\\&=\frac{1}{\sqrt{5}}[(\frac{1+\sqrt{5}}{2})^n×\frac{\sqrt{5}-1}{2}-(\frac{1-\sqrt{5}}{2})^n×\frac{-\sqrt{5}-1}{2}]\\&=\frac{1}{\sqrt{5}}[(\frac{1+\sqrt{5}}{2})^n×\frac{\sqrt{5}-1}{2}+(\frac{1-\sqrt{5}}{2})^n×\frac{\sqrt{5}+1}{2}]\\&=\frac{1}{\sqrt{5}}[(\frac{1+\sqrt{5}}{2})^{n-1}×\frac{1+\sqrt{5}}{2}×\frac{\sqrt{5}-1}{2}+(\frac{1-\sqrt{5}}{2})^{n-1}×\frac{1-\sqrt{5}}{2}×\frac{\sqrt{5}+1}{2}]\\&=\frac{1}{\sqrt{5}}[(\frac{1+\sqrt{5}}{2})^{n-1}×\frac{5-1}{4}+(\frac{1-\sqrt{5}}{2})^{n-1}×\frac{5-1}{4}]\\&=\frac{1}{\sqrt{5}}[(\frac{1+\sqrt{5}}{2})^{n-1}-(\frac{1-\sqrt{5}}{2})^{n-1}]\\&=x_{n-1}\end{aligned}$
即$x_{n+1}-x_n=x_{n-1}$($n$为正整数,且$n≥2$)。