Algebra and Trigonometry 10th Edition

$$-3-\sqrt2i$$
Recall, the conjugate is the value that, when multiplied by the given expression, will yield only real numbers. This means that if the expression is in the form $a+bi$, the conjugate will be $a-bi$. In other words, $b$ will have the opposite sign in the conjugate. Considering this, we find that the conjugate is: $$-3-\sqrt2i$$