Find the product of sqrt (-15) and its conjugate.
Ok, so I am not sure how to do this with a square root involved. Any tips?
That must be a typo. The conjugate of $\displaystyle i\sqrt{15}$ is $\displaystyle -i\sqrt{15}$, of course. Generally speaking a product of conjugates, (a+bi)(a-bi)= $\displaystyle a^2+ b^2$ is the square of the "modulus" of the number. Since $\displaystyle |i\sqrt{15}|= |i||\sqrt{15}|= \sqrt{15}$, that product is 15.