Dividing by a Monomial
Learning Objective(s)
· Divide a monomial by a monomial.
· Divide a polynomial by a monomial.
Introduction
The fourth arithmetic operation is division, the inverse of multiplication. Division of polynomials isn’t much different from division of numbers. Let’s start with dividing a monomial by another monomial, which is the basis for dividing a polynomial by a monomial.
When you multiply two monomials, you multiply the coefficients together and then you multiply the variables together. Similarly, when dividing monomials, you divide the coefficients and then divide variables. When there are exponents with the same base, the law of exponents says you divide by subtracting the exponents. Consider this example:
Example  
Problem  _{} 

 _{}  Group the monomial into numerical and variable factors. 

_{}  Divide the coefficients, and divide the variables by subtracting the exponents of each y term. 
Answer  _{} = _{} 

Here’s another example:
Example  
Problem  A rectangle has an area of 8x^{2 }and a length of 4x. Find the width of the rectangle using the formula: _{}.  
 _{}  Substitute known values. 
 _{}  Divide coefficients, and divide the variables by subtracting the exponents of each x term. 

_{} 

Answer  width = _{} units 

Sometimes division requires simplification.
Example  
Problem  Divide. _{} 

 _{}  Group the monomial into numerical and variable factors. 

_{}  Simplify _{}to _{}. 
 _{}  Divide the variables by subtracting the exponents of r. Note that the variable has a negative exponent. 
 _{}  Simplify _{} by rewriting it as the inverse of r. 
 _{}  Multiply. 
Answer  _{} = _{} 

Remember that a term is not considered simplified if it contains a negative exponent; this is why _{} was rewritten as _{}.
Divide: _{}
A) 11x^{4}
B) 22x^{3}
C) 11x^{3}
D) 22x^{4}

The distributive property states that you can distribute a factor that is being multiplied by a sum or difference, and likewise you can distribute a divisor that is being divided into a sum or difference (as division can be changed to multiplication.)
_{}
Or you can distribute the 2, and divide each term by 2.
_{}
Let’s try something similar with a polynomial.
Example  
Problem  Divide. _{} 


_{}  Distribute 2x over the polynomial by dividing each term by 2x. 
 _{}  Divide each term, a monomial divided by another monomial. 
Answer  _{} = _{} 

Let’s try one more example, watch the signs.
Example  
Problem  Divide. _{} 

 _{}  Divide each term in the polynomial by the monomial. 

_{}  Simplify. Remember that 18 can be written as 18y^{0}. So the exponents are 0 – 1 = −1. 
 _{}  Write the final answer without any negative exponents. 
Answer  _{} = _{} 

Divide: _{}
A) _{}
B) _{}
C) _{}
D) _{}

Summary
To divide a monomial by a monomial, divide the coefficients (or simplify them as you would a fraction) and divide the variables with like bases by subtracting their exponents. To divide a polynomial by a monomial, divide each term of the polynomial by the monomial. Be sure to watch the signs! Final answers should be written without any negative exponents.