Question

why is
19x^-2
not a monomial

thank you

Answer 1

terms are separated by + or - signs
your expression thus has two terms, so it is a binomial

Answer 2

oops. My bad. I read it as 19x - 2
it is a monomial, in the strictest sense of having only one term.
But a monomial is a polynomial with only one term.
polynomials do not have negative exponents.

Answer 3

thank you Oobleck