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Challenge

Investigating Polynomial Sum and Difference

Consider two different polynomials and
Is it possible to calculate the sum and the difference of and Are the obtained results also polynomials? If yes, what is the degree, the leading coefficient, and the constant term of

Discussion

Adding and Subtracting Polynomials

Discussion

Closure Property of Polynomial Addition and Subtraction

Is the result of addition or subtraction of polynomials always another polynomial? This can be verified by analyzing the sum of two arbitrary polynomials.
To add these polynomials, their like terms will be rearranged to be next to each other and then added.
This expression seems to be a polynomial. To show that it is in fact a polynomial, consider a general case of adding two polynomials.
Addition of two polynomials
Note that adding two polynomials comes down to adding their monomials. Since a sum of two or more monomials is always a monomial, the result of adding two polynomials is an expression containing monomials. It is, by definition, a polynomial. Adding or subtracting polynomials results in another polynomial, which means that polynomials are closed under addition and subtraction.

Example

Adding Polynomials in Different Order and Formats

Dylan's family is moving into an apartment. He is curious about how many people live in apartements as opposed to houses. He finds a study that states that during a year period, the amounts of money in millions of dollars spent on buying houses and renting houses by United States residents are modeled by the following two polynomials.

Houses for sale and rental
Here, represents the first year in the year period.
a Calculate Express the polynomial in standard form.
b Calculate Express the polynomial in standard form.
c Compare and Are the sums the same or different?
d What are the degrees of the calculated sums?
What are their leading coefficients?

Hint

a Start by rearranging like terms so that they are situated next to each other.
b Add the polynomials by adding their like terms. Use either the horizontal or vertical format of addition.
c Compare the sums obtained in Parts A and B. Does it matter in which order the polynomials are added?
d Recall the definitions of the degree and the leading coefficient of a polynomial.

Solution

a In order to add the two given polynomials, rearrange the terms so that like terms are next to each other. Then, add the like terms and simplify the sum.
Note that the polynomial is written in standard form as the degrees of its monomials decrease moving from left to right.
b To find the sum of the polynomials will be added using the vertical format of polynomial addition. Again, the sum can be found by adding the like terms of the polynomials. To perform the addition correctly, do not forget to align the like terms vertically.
c Now, the sums found in Parts A and B can be compared.
As can be seen, these sums are the same polynomial. Recall that addition of real numbers is commutative. Since adding polynomials comes down to adding the coefficients of like terms, which are real numbers, it can be concluded that the addition of polynomials is also commutative.
d Recall that the degree of a polynomial is the highest degree of its monomials. In this case, the first monomial has the which is
Therefore, the degree of this polynomial is The leading coefficient of a polynomial is the coefficient of the term with the highest degree. Since the first term has the highest degree, the is

Example

Subtracting Polynomials to Solve a Real-Life Problem

Dylan is delighted to find out that one of his classmates lives in his apartment building, although they live on different floors. They decided to run a little experiment for their science class. Both of them would drop an object from their window at the same time and would see whose object reached the ground first.
Teddy bear and pencil are dropped from different height
External credits: @freepik
The following two polynomials and represent the height of the teddy bear and the pencil seconds after being released, respectively.
a Write the simplified polynomial that represents the difference between the heights of the teddy bear and the pencil seconds after being dropped.
b Calculate Express the polynomial in standard form.
c Compare and Are these differences the same or different?
d What are the degrees of the calculated differences?
What are their leading coefficients?

Hint

a First, rearrange the like terms so that they are situated next to each other, then add them.
b Subtract the polynomials by subtracting their like terms. Use either the horizontal or vertical format of subtraction.
c Compare the results obtained in Parts A and B. Does the order in which the polynomials are subtracted matter?
d Use the definitions of the degree and the leading coefficient of a polynomial.

Solution

a To subtract the two given polynomials, rearrange the terms so that like terms are next to each other. Next, add the like terms and simplify the difference.
b To find the polynomial that represents the difference align the like terms of the polynomials vertically and then subtract them.
c Now, the differences found in Parts A and B can be compared.
The polynomials are different. This suggests that when subtracting polynomials, their order does matter. In other words, the subtraction of polynomials is not commutative.
d To determine the of the polynomials, look for the highest degree of their monomials.
The degree of each polynomial is Next, recall that the leading coefficient of a polynomial is the coefficient of the term with the highest degree.
In the first polynomial, the leading coefficient is while it is in the second polynomial.

Pop Quiz

Determining the Degree and Leading Coefficient of Polynomials

Consider the sum or difference of the given polynomials. Identify their degree or leading coefficient.

Two different polynomials are generated randomly