Quadratics and roots

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The question I am trying to solve is this:

$4 x^2 - 3 x - 3 = 0$ has roots $p, q$. Find all quadratic equations with roots $p^3$ and $q^3$.

I was able to answer this question by simply finding the roots of the equation using the quadratic formula ($p = -0.5687...$ and $q = 1.3187...$), cubing it, and then plugging it in as $a(x - p)(x - q)$.

This seems to work, however is quite ugly, and is not exact.

The correct answer, according to my textbook, is $a(64 x^2 - 135 x - 27)$, but I can't work out how it got that answer.

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Use Vieta's formula to find $\displaystyle p+q=\frac34,pq=-\frac34$

Now, $\displaystyle p^3+q^3=(p+q)^3-3pq(p+q), p^3q^3=(pq)^3$