Answer
$$\frac{a^2b^2}{2}-2$$
Work Step by Step
We use the equation for the area of a triangle to find:
$$ A=\frac{1}{2}bh \\ A=\frac{1}{2}\left(ab-2\right)\left(ab+2\right) \\ A=\frac{1}{2}\left(a^2b^2-4\right) \\ A= \frac{a^2b^2}{2}-2$$
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