First, if we have a polynomial that the form is as follow
P(x,y)=a1x^n-1y^p-1+ a2x^n-2y^p-2 + . . . . + a0xy+c, the degree can be found with the sum of the highest value of power of each term. If the number of term is 3, it is called trinom, if it is 2, the polynomial is called binom. So in our case, 0– 5xy3 + 9x2y is a binom with a degree of 4, because number of term 2, degree =1 + 2 =3, upper than 2+ 1(the second term)
4xy^3– 5xy3 + 9x2y = -xy3 +9x2y, binome degree 4, and the last possibility is 9x^2 y – 5xy3 + 9x2y =18x^2 y – 5xy3, binome degree 4
