Help with how to show aritmetic progression question. How can I show that if $(\chi_{n})$ is a aritmetic progression, then:
$$\frac{1}{ \sqrt{\chi_{1}} + \sqrt{\chi_{2}} } +
 \frac{1}{ \sqrt{\chi_{2}} + \sqrt{\chi_{3}} } + \cdots +
\frac{1}{ \sqrt{\chi_{n-1}} + \sqrt{\chi_{n}} } = 
\frac{n-1}{ \sqrt{\chi_{1}} + \sqrt{\chi_{n}} }
              $$

$ \frac{1}{ \sqrt{\chi_{1}} + \sqrt{\chi_{2}} } +
 \frac{1}{ \sqrt{\chi_{2}} + \sqrt{\chi_{3}} } + \cdots +
\frac{1}{ \sqrt{\chi_{n-1}} + \sqrt{\chi_{n}} } = \frac{\sqrt{\chi_{2}} - \sqrt{\chi_{1}} }{ \chi_2-\chi_1 } + \frac{\sqrt{\chi_{3}} - \sqrt{\chi_{2}} }{ \chi_3-\chi_2 } + \cdots +
\frac{\sqrt{\chi_n}-\sqrt{\chi_{n-1}}}{ \chi_{n}-\chi_{n-1} } $
But $\chi_i-\chi_{i-1}=d$, the common difference of the arithmetic sequence.
$\frac{\sqrt{\chi_{2}} - \sqrt{\chi_{1}} }{ \chi_2-\chi_1 } + \frac{\sqrt{\chi_{3}} - \sqrt{\chi_{2}} }{ \chi_3-\chi_2 } + \cdots +
\frac{\sqrt{\chi_n}-\sqrt{\chi_{n-1}}}{ \chi_{n}-\chi_{n-1} }=\frac{1}{d}\{\sqrt{\chi_{2}} - \sqrt{\chi_{1}}+\sqrt{\chi_{3}} - \sqrt{\chi_{2}}+\cdots+\sqrt{\chi_{n}} - \sqrt{\chi_{n-1}}\}$
$=\frac{\sqrt{\chi_{n}} - \sqrt{\chi_{1}}}{d}$
But since $\chi_n=\chi_1+(n-1)\cdot d$, we have $\frac{1}{d}=\frac{n-1}{\chi_n-\chi_1}$
Hence $\frac{\sqrt{\chi_{n}} - \sqrt{\chi_{1}}}{d}=\frac{(n-1)\cdot {\left(\sqrt{\chi_{n}} - \sqrt{\chi_{1}}\right)} }{\chi_n-\chi_1}=\frac{n-1}{\sqrt{\chi_{1}} + \sqrt{\chi_{n}}}$
