Question

9-8x^2+2x^4 is this a trinomial​

Answer 1

Yes. A monomial is a term composed by a coefficient and powers of variables multiplied with each other, for example

$3xy^3z^2$

is a monomial.

In your case, the monomials are

$9,\quad 8x^2,\quad 2x^4$

As the name suggests, a trinomial is the sum of three monomials, which is exactly your case.