How to Solve Polynomials With Degree of 3

A third-degree polynomial is an equation that has a maximum degree of three attached to any variable or number. Factoring by grouping is the easiest way to solve an equation of this nature. Be sure to follow all directions closely, and do not forget to enter your answers back into the equation to test the validity of your answers before listing them in set notation form.

Instructions

    • 1

      Place all non-zero terms in the equation to one side, and set the entire equation equal to zero. The equation x^3+x^2=4x+4 would become x^3+x^2-4x-4=0.

    • 2

      Use factor by grouping to combine terms that have a common factor. The equation in Step 1 would be grouped as follows: (x^3+x^2)+(-4x-4)=0. Then, simplify the equation by factoring it: x^2(x+1)-4(x+1)=0.

    • 3

      Set each factored group equal to zero: x^2-4=0 or x+1=0.

    • 4

      Solve the equations in Step 3 individually. Solving the equation x+1=0 would yield x=-1. Solving the equation x^2-4=0 would yield x= +or- 2.

    • 5

      Plug all of the answers calculated in Step 4 back into the equation individually to test if they are solutions to the equation. The equation for the solution of -2 would be: -2^3+-2^2=4(-2)+4. Since both sides of the equation equal -4, -2 is a solution. The equation for the solution of -1 would be: (-1)^3+(-1)^2=4(-1)+4. Since both sides of the equation equal 0, -1 is a solution. The equation for the solution of 2 would be: (2)^3+(2)^2=4(2)+4. Since both sides of the equation equal 12, 2 is a solution.

    • 6

      List your answer as a solution set. For this problem, all of the solutions calculated in Step 4 are verifiable and, therefore, are solutions. The set notation for this problem would be {-2,-1,2}.

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