Originally Posted by

**dkaksl** Not sure about the first one. But I think I got the second one for you.

$\displaystyle \frac{(7-5\sqrt2)}{(7+5\sqrt2)(7-5\sqrt2)}$

$\displaystyle \frac{(7-5\sqrt2)}{(7)^2-(5\sqrt2)^2}$

$\displaystyle \frac{(7-5\sqrt2)}{49-50}$

$\displaystyle \frac{(7-5\sqrt2)}{-1}$

$\displaystyle -7+5\sqrt2$

Basically, you multiply and divide by the same thing. In the case of making the denominator (lower part of the fraction) simple, you multiply both nominator and denominator with $\displaystyle (7-5\sqrt{2})$

Edit: Wait, you sure the book says $\displaystyle \sqrt5$ for the answer?