(3 di 4)
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$\small \left(a+y-2\right)\left(a+y+2\right)-\left(a-y\right)^2-4\left(ay-1\right)+1 = $
$\small = a^2+ay+\cancel{2a}+ay+y^2+\cancel{2y}-\cancel{2a}-\cancel{2y}-4-\left(a^2-2ay+y^2\right)-4ay+4+1 = $
$\small = \cancel{a^2}+2ay+\cancel{y^2}-4-\cancel{a^2}+2ay-\cancel{y^2}-4ay+5 = $
$\small = 2ay-4+2ay-4ay+5 = $
$\small = \left(2+2-4\right)ay+1 = $
$\small = 0ay+1 = $
$\small = +1 $