Answer
$4$.
1 positive real zero.
1 negative real zero.
Work Step by Step
Step 1. Based on the given function, we have degree $n=4$, thus the maximum number of real zeros that the polynomial function may have is $4$.
Step 2. As there is 1 sign change in $f(x)$, based on the Descartes’ Rule of Signs, there will be 1 positive real zero.
Step 3. $f(-x)=5x^4+2x^2+6x-5$ and there is 1 sign change in $f(-x)$, thus there will be 1 negative real zero.