Khan Academy
Khan Academy: Polynomial Basics: Subtracting Polynomials With Multiple Variables
This video demonstrates how to subtract polynomials when there are multiple variables in each polynomial.
Khan Academy
Khan Academy: Polynomials: Addition and Subtraction of Polynomials
This video explains how to determine the degree of a polynomial, shows how to add and subtract polynomials, and shows how to write polynomial expressions to represent the area of given shapes.