Which is true about the polynomial 18r2s + 6r – 7s2?
it is a binomial with a degree of 2.
it is a binomial with a degree of 3.
it is a trinomial with a degree of 2.
it is a trinomial with a degree of 3.

If the form of the polynomial is like x^ny^p+x^n-1y^p-1+ . . . +xy+c, to find the degree of such polynomial is as follow: the sum of the degree of the first term; in our case, we have 18r²s+6r-7s², the first term is 18r²s=18r²s^1, the sum of the degree is 2+1=3, besides, there exists three terms, 18r²s, 6r, -7s², the polynomial is a trinom, so the true answer is D, it is a trinomial with a degree 3

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