Section 8.2 Algebraic Fractions
Subsection 1. Factor a polynomial
To reduce an algebraic fraction, we must factor its numerator and denominator.
Subsubsection Examples
Example 8.13.
Factor.
- \(\displaystyle 4x^2-4x\)
- \(\displaystyle 4x^2-1\)
- \(\displaystyle 4x^2-4x+2\)
We factor out a common factor of \(4x\) to get \(4x(x-1)\text{.}\)
This is a difference of two squares that factors as \((2x-1)(2x+1)\text{.}\)
This is the square of a binomial, \((2x-1)^2\text{.}\)
Example 8.14.
Factor.
- \(\displaystyle 27a^2-3\)
- \(\displaystyle 27a^3-1\)
- \(\displaystyle 81a^3-a\)
We first factor out 3 to find \(3(9a^2-1)\text{,}\) then factor the difference of two squares to get \(3(3a-1)(3a+1)\text{.}\)
This is a differece of two cubes, which factors as \((3a-1)(9a^2+3a+1)\text{.}\)
We first factor out \(a\) to get \(a(81a^2-1)\text{,}\) then factor the difference of two squares to get \(a(9a-1)(9a+1)\) .
Subsubsection Exercises
Checkpoint 8.15.
Factor completely \(2x^3+16y^3\)
Checkpoint 8.16.
Factor completely \(4x^2y-36y^3\)
Checkpoint 8.17.
Factor completely \(2b^3-6b^2-36b\)
Checkpoint 8.18.
Factor completely \(9b^4+9b^2\)
Subsection 2. Find the opposite of a binomial
To find the opposite or negative of a binomial we multiply by \(-1\text{.}\)
Subsubsection Examples
Example 8.19.
Which of these is the opposite of \(m^2-p~\text{?}\)
- \(\displaystyle m^2+p\)
- \(\displaystyle m-p^2\)
- \(\displaystyle p-m^2\)
The opposite of \(m^2-p\) is \(-(m^2-p) = -m^2+p\text{,}\) or \(p-m^2\text{.}\)
Example 8.20.
Which of these pairs of binomials are opposites?
- \(3c-5\) and \(5+3c\)
- \(5-3c\) and \(3-5c\)
- \(5c-3\) and \(3-5c\)
The opposite of \(5c-3\) is \(-(5c-3)=-5c+3\text{,}\) or \(3-5c\text{,}\) so (c) is correct.
Subsubsection Exercises
Checkpoint 8.21.
Find the opposite of the binomial \(2x+1\)
Checkpoint 8.22.
Find the opposite of the binomial \(b^2-b\)
Checkpoint 8.23.
Find the opposite of the binomial \(-4n+8\)
Checkpoint 8.24.
Find the opposite of the binomial \(-3z^2-2\)
Subsection 3. Use horizontal and vertical lines
The asymptotes of rational functions are horizontal and vertical lines.
Subsubsection Examples
Example 8.25.
Give the equation and slope of the line.
This line is a vertical line. All the points on the line have \(x\)-coordinate \(-15\text{,}\) so the equation of the line is \(x=-15\text{.}\) Because \(\Delta x=0\) between any two points on the line, its slope is undefined.
Example 8.26.
Give the equation and slope of the line.
This line is a horizontal line. All the points on the line have \(y\)-coordinate \(04\text{,}\) so the equation of the line is \(y=40\text{.}\) Because \(\Delta y=0\) between any two points on the line, its slope is \(0\text{.}\)
Subsubsection Exercises
Checkpoint 8.27.
Give the equation and slope of the line.
Checkpoint 8.28.
Give the equation and slope of the line.
Checkpoint 8.29.
Give the equation and slope of the line.
Checkpoint 8.30.
Give the equation and slope of the line.