A polynomial of one-variable is given by following expression :-
[tex] Ax^n + Bx^{n-1} +Cx^{n-2}+Dx^{n-3}+Ex^{n-4}+..... [/tex]
where A, B, C, D, E are the coefficients of terms in the polynomial and x is variable of the equation.
A is the leading coefficient and it can not be zero i.e. A≠0.
n is the degree of the polynomial.
It says to write a trinomial in one variable of degree 5.
Trinomial means only three terms with non-zero coefficients, and degree 5 means n = 5.
There could be many answers, but an example of "trinomial of degree 5" would be :-
[tex] Ax^5 + Bx^4 + Cx^3 [/tex]
[tex] 3x^5 + 5x^4 + 2x^3 [/tex]