Rationalize the denominator of the surd, giving your answer in the simplest form. Rationalize the denominator of the surd, giving your answer in the simplest form.
$\frac {3}{\sqrt2+5} $
Please help me...
It must be like this right?
$\frac {3}{\sqrt2+5} * \frac{\sqrt2-5}{\sqrt2-5}$ 

Yes. in general we do not leave the denominator irrational. So we multiply and divide the fraction by the conjugate of denominator.
In this case the conjugate of $\sqrt{2}+5$ is $\sqrt{2}-5$.
$$\frac{3(\sqrt{2}-5)}{(\sqrt{2}+5)(\sqrt{2}-5)}$$
$$\frac{3\sqrt 2 - 15}{2-25} = \frac{3\sqrt 2 - 15}{-23}$$
$$\frac{15 - 3\sqrt{2}}{23}$$
