How do you determine the binomial factors of #x^3+3x^2+3x+1#?

1 Answer
May 28, 2017

#(x+1)^3#

Explanation:

Using the rational root theorem gives:

#p = 1, q=1#

All values of #+-p/q# are #-1# and #1#.

Now, plug in each value to the polynomial. By the remainder theorem, if the output is zero, the input must be a root.

#(-1)^3+3(-1)^2+3(-1)+1=-1+3-3+1 = 0#
#therefore# there is a root at #x = -1#

#(1)^3+3(1)^2+3(1)+1 = 1+3+3+1=8#
#therefore# there is NOT a root at #x=1#

Factors of the polynomial: #(x - "root") = (x-(-1))=(x+1)#
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Now, divide the polynomial by #(x+1)#:

#(x^3+3x^2+3x+1)/(x+1) = (x^3+x^2+x^2+x+x^2+x+x+1)/(x+1)#

#= ((x^3+x^2)+(x^2+x)+(x^2+x)+(x+1))/(x+1)#

#= (x^2 + x + x + 1)#

#= x^2+2x+1#

You could do the same process with this new polynomial, or you could recognize it as a perfect square.

Either way, factoring this polynomial results in #(x+1)^2#

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So the final answer is #(x+1)(x+1)^2 = (x+1)^3#