Answer
Proof given below.
Work Step by Step
We alternatively defined $|x|$ as
$|x|=\sqrt{x^{2}}$
Apply on $x=ab:$
$|ab|=\sqrt{(ab)^{2}}=\sqrt{a^{2}b^{2}}=\sqrt{a^{2}}\cdot\sqrt{b^{2}}=|a|\cdot|b|$
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