Question

= 9x4 − 82x2 + 9 (a) use descartes's rule of signs to determine the possible numbers of positive real zeros of f.

Answer 1

The signs are +-+. There are two sign changes: +- and -+, so Descarte's rule of signs tells you there are 0 or 2 positive real roots.

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A graph tells you there are 2 positive and 2 negative real roots.