To do this, we count the number of sign changes in the polynomial $f(x)=3 x^{4}+5 x^{3}-6 x^{2}+8 x-3$.
The sign changes from positive to negative once (from $+5x^3$ to $-6x^2$), and from negative to positive twice (from $-6x^2$ to $+8x$ and from $+8x$ to $-3$).
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