(questo sarà il primo di tre esercizi)
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$\small = \left(-\dfrac{1}{2}-a\right)\left(\dfrac{1}{2}-a\right)\left(a^2+\dfrac{1}{4}\right)+\left(1-a^2\right)\left(a^2+1\right) =$
$\small = \left(-\dfrac{1}{4}\cancel{+\dfrac{1}{2}a}\cancel{-\dfrac{1}{2}a}+a^2\right)\left(a^2+\dfrac{1}{4}\right)\cancel{+a^2}+1-a^4\cancel{-a^2} =$
$\small = \cancel{-\dfrac{1}{4}a^2}-\dfrac{1}{16}\cancel{+a^4}\cancel{+\dfrac{1}{4}a^2}+1\cancel{-a^4} =$
$\small = -\dfrac{1}{16}+1 =$
$\small = \dfrac{-1+16}{16} =$
$\small = \dfrac{15}{16} $