TITLE: How to show $\sqrt{4+2\sqrt{3}}-\sqrt{3} = 1$
QUESTION [10 upvotes]: I start with $x=\sqrt{4+2\sqrt{3}}-\sqrt{3}$, then
$\begin{align*}
x +\sqrt{3} &= \sqrt{4+2\sqrt{3}}\\
(x +\sqrt{3})^2 &= (\sqrt{4+2\sqrt{3}})^2\\
x^2 + (2\sqrt{3})x + 3 &= 4+ 2\sqrt{3}\\
x^2 + (2\sqrt{3})x - 1 - 2\sqrt{3} &= 0
\end{align*}$
So I have shown that there is some polynomial whose solution is $x=\sqrt{4+2\sqrt{3}}-\sqrt{3}$, but I have not shown it to be 1.

REPLY [6 votes]: It is useful, when approaching a problem like this, to eliminate the more complex square roots. So given:
$$\sqrt{4 + 2 \sqrt{3}} - \sqrt{3} = 1$$
Rearrange to (so as to isolate the more complex square root on the LHS):
$$\sqrt{4 + 2 \sqrt{3}} = \sqrt{3} + 1$$
Square both sides:
$$4 + 2 \sqrt{3} = (\sqrt{3} + 1)(\sqrt{3} + 1)$$
Multiply out the RHS:
$$4 + 2 \sqrt{3} = 3 + 2\sqrt{3} + 1$$
So
$$4 + 2 \sqrt{3} = 4 + 2\sqrt{3}$$
This does not rely on you seeing the factorization, you just methodically work on simplifying the expression you were given.