Simplify the surds below. Simplify this:
$10 + 2\sqrt5 - 4\sqrt2\sqrt5 - 4\sqrt2$
Help please! $:'($
It came out like this:
$10 + 2\sqrt5 -4\sqrt10 - 4\sqrt2$
How should I do the next step? Um stuck.

Note that $4 \sqrt{10} = 4 \sqrt 2\cdot\sqrt 5$, and $10 = 2\sqrt 5\cdot \sqrt 5$.
Hint: FACTOR!
$$\begin{align} 10 + 2\sqrt5 - \color{red}{4\sqrt2}\sqrt5 - \color{red}{4\sqrt2} & = \color{blue}{2\sqrt 5}\cdot \sqrt 5 + \color{blue}{2\sqrt 5} - \color{red}{4\sqrt 2}(\sqrt 5 + 1)\\ \\ & = \color{blue}{2\sqrt 5}\color{purple}{\bf (\sqrt 5 + 1)} - 4\sqrt 2\color{purple}{\bf (\sqrt 5 + 1)}\\ \\ & = \;\;\cdots \end{align}$$
