Zero Factor Property

Key Questions

  • You use the zero factor property after you have factored the quadratic to find the solutions.

    It is best to look at an example: #x^2+x-6=0#

    This factors into:

    #(x+3)(x-2)=0#

    We find our solutions by setting each factor to zero and solve:

    #x+3=0#
    #x=-3#

    or

    #x-2=0#
    #x=2#

    Previous answer (I was thinking some more complicated before):

    You are not using the words precisely. You use the factor theorem with the factor property. The factor theorem states that if you find a #k# such that #P(k)=0#, then #x-k# is a factor of the polynomial. The factor property states that #k# must a factor of the constant term in #P(x)#.

    Having said all that, you wouldn't normally use the factor theorem or factor property to solve a quadratic; they are many used to find factors of higher order polynomials. Once you reduce the higher order polynomial to a quadratic, you use regular factoring methods such as FPS or PFS: Factors, Product, and Sum.

    #P(x)=ax^2+bx+c#

    The problem with the factor theorem and factor property is that it's not as easy to use when #a!=1#.

  • Answer:

    Well, if you a polynomial is factorable then its roots/zeroes can be easily found by setting it to zero and using the zero factor property. Please see explanation below.

    Explanation:

    The Zero Product Property:
    A product of factors is zero if and only if one or more of the factors is zero. Or:
    if #a*b = 0#, then either #a = 0# or #b = 0# or both.
    Example: Find the roots of the polynomial by factoring:
    #P(x) = x^3-x^2-x+1#, set to zero:
    #x^3-x^2-x+1=0#, factor by grouping:
    #x^2(x-1)-1(x-1)=0#
    #(x^2-1)(x-1)=0#, use difference of squares to factor further:
    #(x+1)(x-1)(x-1)=0#, use the zero factor property:
    #x+1=0=>x=-1#
    #x-1=0=>x=1#
    Notice that #x = 1# has a multiplicity of 2.

  • The zero factor property states that if #ab=0#, then either #a=0# or #b=0#.

    Example: find the roots of #x^2-x-6#.

    #x^2-x-6=0#

    #(x-3)(x+2)=0#

    Now, the zero factor property can be applied, since two thing are being multiplied and equal zero.

    We know that either

    #x-3=0color(white)(ssss)# or #color(white)(ssss)x+2=0#

    Solve both to find that #x=3# or #x=-2#.

Questions