<s>[INST] How to Simplify $\sqrt {-X} \times \sqrt {-Y}$ For example : $\sqrt {-18} \times \sqrt {-12}$
Would I start by multiplying the 2 numbers under a square root, In which case the double negatives cancel out? 
$ \sqrt {-18\times-12} = \sqrt {216} = 6\sqrt {6}$
Or get the i out of the square roots in which case I get a  $i^2$?
$$ \sqrt {18}i \times \sqrt {12}i =  6\sqrt {6}i^2 = - 6\sqrt {6}$$
 [/INST] Simply
$$i\sqrt{18}\cdot i\sqrt{12}$$
$$-1\sqrt{12\cdot 18}$$
$$-1\sqrt{216}$$
$$-6\sqrt{6}$$
ALWAYS start with $i$
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