Issues with re-arranging this formula

Question

I am needing to put the formula $(\sqrt5+\sqrt7)(\sqrt5-\sqrt7)$ into the form $a+b\sqrt{c}$

Although it looks fairly simple, I do not know where to start with this. Please could someone explain the methodology to me so that I can learn to get to the correct answer ? This would be very much appreciated .

Answer 1

$(\sqrt5+\sqrt7)(\sqrt5-\sqrt7)=5-7=-2=-2+0\cdot\sqrt \pi$

Answer 2

We have

$(\sqrt5+\sqrt7)(\sqrt5-\sqrt7) = 5-7 = -2$

which you can also write as $-2 + 1\sqrt{0}$