SOLUTION: Show that (x-2) is a factor of f(x) = x³-2x²-4x+8. Hence factorise f(x) completely.

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Question 1132054: Show that (x-2) is a factor of f(x) = x³-2x²-4x+8.
Hence factorise f(x) completely.

Found 2 solutions by Boreal, ikleyn:
Answer by Boreal(15235) About Me  (Show Source):
You can put this solution on YOUR website!
Can use synthetic division with 2
2/1--- -2---- -4-----8
1 0 -4 0
that is x^2-4
so the factors are (x-2)(x^2-4) or (x-2)(x-2)(x+2), or (x-2)^2*(x+2)
graph%28300%2C300%2C-10%2C10%2C-10%2C10%2Cx%5E3-2x%5E2-4x%2B8%29

Answer by ikleyn(52945) About Me  (Show Source):
You can put this solution on YOUR website!
.
This problem is to use the "Remainder theorem".



The Remainder theorem says that the binomial (x-a) is a factor of a polynomial

    f(x) = a%5B0%5D%2Ax%5En+%2B+a%5B1%5D%2Ax%5E%28n-1%29+%2B+ellipsis+%2B+a%5Bn-1%5D%2Ax+%2B+a%5Bn%5D

if and only if the value of "a" is the root of the polynomial f(x), i.e. f(a) = 0.



So, in your case, to show that (x-2) is a factor of the given polynomial 

    f(x) = x%5E3+-+2x%5E2+-+4x+%2B+8,

you need simply calculate


    f(5) = 2%5E3+-+2%2A2%5E2+-+4%2A2+%2B+8 = 8 - 8 - 8 + 8 = 0


and make sure that it is equal to zero.

Solved.

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See the lessons
    - Divisibility of polynomial f(x) by binomial x-a and the Remainder theorem
    - Solved problems on the Remainder thoerem
in this site.


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    ALGEBRA-II - YOUR ONLINE TEXTBOOK.

The referred lessons are the part of this online textbook under the topic
"Divisibility of polynomial f(x) by binomial (x-a). The Remainder theorem".

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Free of charge online textbook in ALGEBRA-I
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