The following is a question that I composed and solved.
I want to know if it is mathematically correct and well-formatted.
Question
Show that $\root{3}\of{\sqrt{5}+2}+\root{3}\of{\sqrt{5}-2}=\sqrt{5}$
Answer
Guess that: $\root{3}\of{\sqrt{5}\pm 2}=a\pm b$
Then $\root{3}\of{\sqrt{5}+2}+\root{3}\of{\sqrt{5}-2}=$
$(a+b)+(a-b)=2a=\sqrt{5} \implies a=\frac{1}{2}\sqrt{5}$
Using $a=\frac{1}{2}\sqrt{5}$, we make a revised guess:
$\root{3}\of{\sqrt{5}\pm 2}=\frac{1}{2}\sqrt{5}\pm c$
Now solve for c:
$\begin{align} \left(\root{3}\of{\sqrt{5}\pm 2}\right)^3&=\left(\frac{1}{2}\sqrt{5}\pm c\right)^3 \\ \sqrt{5}\pm 2&=\left(\frac{3}{2}c^2+\frac{5}{8}\right)\sqrt{5}\pm\left(c^3+\frac{15}{4}c\right) \\ \end{align}$
Equating the irrational and rational parts,
we get a system of 2 equations:
(1) $\quad \frac{3}{2}c^2+\frac{5}{8}=1 \implies c=\pm \frac{1}{2}$
(2) $\quad c^3+\frac{15}{4}c=2 \implies$ Only $c=\frac{1}{2}$ works
So $\root{3}\of{\sqrt{5}\pm 2}=\frac{1}{2}\sqrt{5}\pm \frac{1}{2}$
Finally, $\root{3}\of{\sqrt{5}+2}+\root{3}\of{\sqrt{5}-2}=$
$\left(\frac{1}{2}\sqrt{5}+\frac{1}{2}\right)+\left(\frac{1}{2}\sqrt{5}-\frac{1}{2}\right)=\sqrt{5}$
Q. E. D.