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Study Guides > College Algebra CoRequisite Course

Introduction to Factoring Polynomials

Learning Outcomes

By the end of this section, you will be able to:
  • Identify and factor the greatest common factor of a polynomial.
  • Factor a trinomial with leading coefficient 1.
  • Factor by grouping.
  • Factor a perfect square trinomial.
  • Factor a difference of squares.
  • Factor a sum and difference of cubes.
  • Factor an expression with negative or fractional exponents.
Imagine that we are trying to find the area of a lawn so that we can determine how much grass seed to purchase. The lawn is the green portion in the figure below. A large rectangle with smaller squares and a rectangle inside. The length of the outer rectangle is 6x and the width is 10x. The side length of the squares is 4 and the height of the width of the inner rectangle is 4. The area of the entire region can be found using the formula for the area of a rectangle.

A=lw=10x⋅6x=60x2 units2\begin{array}{ccc}\hfill A& =& lw\hfill \\ & =& 10x\cdot 6x\hfill \\ & =& 60{x}^{2}{\text{ units}}^{2}\hfill \end{array}

The areas of the portions that do not require grass seed need to be subtracted from the area of the entire region. The two square regions each have an area of A=s2=42=16A={s}^{2}={4}^{2}=16 units2. The other rectangular region has one side of length 10x−810x - 8 and one side of length 44, giving an area of A=lw=4(10x−8)=40x−32A=lw=4\left(10x - 8\right)=40x - 32 units2. So the region that must be subtracted has an area of 2(16)+40x−32=40x2\left(16\right)+40x - 32=40x units2. The area of the region that requires grass seed is found by subtracting 60x2−40x60{x}^{2}-40x units2. This area can also be expressed in factored form as 20x(3x−2)20x\left(3x - 2\right) units2. We can confirm that this is an equivalent expression by multiplying. Many polynomial expressions can be written in simpler forms by factoring. In this section, we will look at a variety of methods that can be used to factor polynomial expressions.

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