Answer
$\pm 2i, \pm 3i$
Step 2. We have $f(x)=(x+3i)(x-3i)(x+2i)(x-2i)$
Work Step by Step
Step 1. $f(x)=x^4+13x^2+36=(x^2+9)(x^2+4)$, thus the zeros are $x=\pm 3i, \pm 2i$
Step 2. We have $f(x)=(x+3i)(x-3i)(x+2i)(x-2i)$
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