Middle School Math Solutions – Polynomials Calculator, Multiplying Polynomials

Multiplying polynomials can be tricky because you have to pay attention to every term, not to mention it can be very messy. There are a few ways of multiplying polynomials, depending on how many terms are in each polynomial. In this post, we will focus on how to multiply two term polynomials and how to multiply two or more term polynomials.

Multiply two term polynomials

When multiplying polynomials with two terms, you use the FOIL method. The FOIL method only works for multiplying two term polynomials. FOIL stands for first, outer, inner, last. This lets you know the order of how to distribute and multiply the terms. Let’s see how it works.

After FOILing, multiply the terms, group like terms, and add like terms if there are any.
Here is another helpful identity to use when multiplying two term polynomials:

(a+b)(a-b)=a^2-b^2

Multiplying these polynomials is pretty simple because if you memorize these identities then you just plug in the values and have an answer.

Multiplying multiple term polynomials

You cannot use the FOIL method to multiply these polynomials. Instead, you have to multiply each term in one polynomial by each term in the other. You can do this by multiplying each term of one polynomial by the other polynomial. This can be tricky because it is easy to miss one term. When we do examples of this, it will become easier to understand how to solve them.

When multiplying polynomials, you may come across multiplying variables with exponents by variables with exponents. In this case, we use this exponent rule:

x^n\cdot x^m=x^(n+m)

For this rule, the base or variable must be the same. When multiplying variables with exponents, you add the exponents together.


Let’s see some examples to understand how to multiply polynomials.
First example (click here):

(2x-1)(5x-6)

We will use the FOIL method to solve this.
1.   Use FOIL identity

(2x-1)(5x-6)
2x\cdot 5x+2x\cdot -6+(-1)\cdot 5x+(-1)\cdot -6

2.   Multiply terms

10x^2-12x-5x+6

3.   Group like terms

10x^2-12x-5x+6

 (Luckily, everything was already grouped together)

4.   Add like terms

10x^2-17x+6

Next example (click here):

(2x^2+6)(2x^2-6)

Here, we can use another one of the identities for multiplying two term polynomials.
1.   Use (a+b)(a-b)=a^2-b^2

(2x^2+6)(2x^2-6)
(2x^2 )^2-6^2

2.   Simplify

4x^4-6^2
4x^4-36

Last example (click here):

(x^2+2x-1)(2x^2-3x+6)

1.   Multiply each term in one polynomial by the other polynomial

x^2 (2x^2-3x+6)+2x(2x^2-3x+6)-1(2x^2-3x+6)

2.   Distribute and multiply

2x^2\cdot x^2-3x\cdot x^2+6\cdot x^2+2x^2\cdot 2x-3x\cdot 2x+6\cdot 2x+2x^2\cdot -1-3x\cdot -1+6\cdot -1
2x^4-3x^3+6x^2+4x^3-6x^2+12x-2x^2+3x-6

3.   Group like terms

2x^4-3x^3+6x^2+4x^3-6x^2+12x-2x^2+3x-6
2x^4-3x^3+4x^3+6x^2-6x^2-2x^2+12x+3x-6

4.   Add like terms

2x^4+x^3+6x^2-6x^2-2x^2+12x+3x-6
2x^4+x^3-2x^2+12x+3x-6
2x^4+x^3-2x^2+15x-6

Multiplying polynomials looks intimidating, but as long as you keep your work neat and double check your work, it should be pretty easy. Practice will be one of the biggest things that will help you. The more you practice, the easier multiplying polynomials will be because you will get the hang and flow of how to multiply them. Check out Symbolab’s Practice for more help and practice.

Until next time,

Leah

Middle School Math Solutions – Polynomials Calculator, Subtracting Polynomials

In the previous post, we talked about how to add polynomials. In this post, we will talk about subtracting polynomials. The key to subtracting polynomials is to make sure that you distribute the minus sign to the expression in the parentheses. Imagine that instead of – there is a -1. This should help you visualize why you are distributing the minus sign. Once the minus sign is distributed, the minus sign will turn into a plus sign. Then, you’ll be able to add the polynomials together. Let’s see the steps for subtracting polynomials.

Steps: 

1. Distribute the negative sign
• Include this step only if there is a minus sign in front of a polynomial in parentheses
2. Remove the parentheses
• Include this step if there are polynomials in parentheses
3. Group like terms
• Put together and order like terms (terms with the same variables and the same exponent)
4. Add like terms 
• Add the coefficients of the like terms

Let’s see some examples to better understand distributing the minus sign.



First example (click here):

(x^2+2x-1)-(2x^2-3x+6)

1.  Distribute the negative sign

(x^2+2x-1)-(2x^2-3x+6)
(x^2+2x-1)-1(2x^2-3x+6)
(x^2+2x-1)+(-2x^2+3x-6)

When we imagine that there is a -1 instead of – outside the parentheses, it is easy to see and remind ourselves that we have to distribute the negative. Distributing the negative sign allows that minus sign to turn into a plus sign.

2.   Remove the parentheses

x^2+2x-1+-2x^2+3x-6
x^2+2x-1-2x^2+3x-6

3.  Group like terms

x^2+2x-1-2x^2+3x-6
x^2-2x^2+2x+3x-1-6

4.  Add like terms

x^2-2x^2+2x+3x-1-6
-x^2+5x-7

Second example (click here):

(2x^3+2x-1)-(2x^2-5x-6)

1.  Distribute the negative sign

(2x^3+2x-1)-(2x^2-5x-6)
(2x^3+2x-1)-1(2x^2-5x-6)
(2x^3+2x-1)+(-2x^2+5x+6)

2.  Remove the parentheses

2x^3+2x-1+-2x^2+5x+6
2x^3+2x-1-2x^2+5x+6

3.  Group like terms

2x^3+2x-1-2x^2+5x+6
2x^3-2x^2+2x+5x-1+6

4.  Add like terms

2x^3-2x^2+7x-1+6
2x^3-2x^2+7x+5

Last example (click here):

(4x^3-x^2+x-2)-(-x^2+3)

1.  Distribute the negative sign

(4x^3-x^2+x-2)-(-x^2+3)
(4x^3-x^2+x-2)-1(-x^2+3)
(4x^3-x^2+x-2)+(x^2-3)

2.  Remove the parentheses

4x^3-x^2+x-2+x^2-3

3.  Group like terms

4x^3-x^2+x-2+x^2-3
4x^3-x^2+x^2+x-2-3

4.  Add like terms

4x^3+x-2-3
4x^3+x-5

Subtracting polynomials takes some practice to get the hang of distributing and remembering to distribute. Once you’ve mastered adding polynomials, subtracting them should be simple. For more practice, check out Symbolab’s Practice.

Until next time,

Leah