Why is 12ab - 3ab^2 cubic? By its degree.?

The degree of "a" is 1. The degree of b^2 is 2. Those are multiplied together in one term, so we add the degrees. That makes 3.

Karen has it. The degree of a polynomial is determined by the highest sum of exponents in one term.

In 12ab, both a and b have an absentee exponent, which is understood to be 1. Sum of exponents is therefore 2.

In -3ab^2, b has an exponent of 2 while a has the same exponent of 1. Sum of exponents is 2 + 1 = 3, and since this sum is the highest, the degree of the entire polynomial is 3, a cubic.

So, long story short...answer to your query is yes.

The degree is determined by the degree of the term with the highest degree. The degree of 3ab^2 is 3, because one factor of a and 2 factors of b.