I am having difficulty solving these surds problems
$\displaystyle (5+2 \sqrt{7})^2$
and
$\displaystyle \sqrt{8}+\sqrt{18}-\sqrt{50}$
Since we haven't learnt FOIL yet, I understand why you're having trouble with the first one.
If you have two binomials like $\displaystyle (a + b)(c + d)$, they are expanded by multiplying the Firsts, then the Outers, then the Inners, then the Lasts.
So $\displaystyle (a + b)(c + d) = ac + ad + bc + bd$.
So for your first one, you have
$\displaystyle (5 + 2\sqrt{7})^2 = (5 + 2\sqrt{7})(5 + 2\sqrt{7})$
Multiplying the firsts gives $\displaystyle 5 \times 5 = 25$.
Multiplying the outers gives $\displaystyle 5 \times 2\sqrt{7} = 10\sqrt{7}$
Multiplying the inners gives $\displaystyle 5 \times 2\sqrt{7} = 10\sqrt{7}$
Multiplying the lasts gives $\displaystyle 2\sqrt{7}\times 2\sqrt{7} = 4 \times 7 = 28$.
So $\displaystyle (5 + 2\sqrt{7})^2 = 25 + 10\sqrt{7} + 10\sqrt{7} + 28$
$\displaystyle = 53 + 20\sqrt{7}$.
For the second, you need to simplify all of the surds first. Then hopefully you'll have "like surds" that can be collected.
$\displaystyle \sqrt{8} = \sqrt{4 \times 2} = \sqrt{4} \times \sqrt{2} = 2\sqrt{2}$.
$\displaystyle \sqrt{18} = \sqrt{9 \times 2} = \sqrt{9}\times\sqrt{2} = 3\sqrt{2}$.
$\displaystyle \sqrt{50} = \sqrt{25 \times 2} = \sqrt{25}\times\sqrt{2} = 5\sqrt{2}$.
So $\displaystyle \sqrt{8} + \sqrt{18} - \sqrt{50} = 2\sqrt{2} + 3\sqrt{2} - 5\sqrt{2}$
$\displaystyle = 5\sqrt{2} - 5\sqrt{2}$
$\displaystyle = 0\sqrt{2}$
$\displaystyle = 0$.
Chookas for the exam tomorrow.