Answer
$\pm\frac{1}{2},\pm\sqrt 5$
Work Step by Step
Let $y=x^2$, we have
$P(x)=4y^2-21y+5=(4y-1)(y-5)$
The zeros are $y=1/4, 5$
so $x^2=1/4,5$
We have zeros for P as $\pm\frac{1}{2},\pm\sqrt 5$
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