Verified Answer :

A
thinking...
12^2=144
signs different therefore the 12 cancels out (no middle term)
signs different sign is negative

hope this helps

I don't understand what you mean by 'mentally' but anyways, here is how to solve it.

(z−12)(z+12)

=(z+−12)(z+12)

=(z)(z)+(z)(12)+(−12)(z)+(−12)(12)

=z^2+12z−12z−144

=z^2−144

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