Question

Factorise x cube -2x square -5x plus 6

Answer 1

Answer:   {(x + 2), (x - 1), (x - 3)}

Step-by-step explanation:

Presented symbolically, we have:

x^3 - 2x^2 - 5x + 6

Synthetic division is very useful for determining roots of polynomials.  Once we have roots, we can easily write the corresponding factors.  

Write out possible factors of 6:  {±1, ±2, ±3, ±6}

Let's determine whether or not -2 is a root.  Set up synthetic division as follows:

-2   /   1   -2   -5   6

              -2     8   -6

     -----------------------

        1     -4      3    0

since the remainder is zero, we know for sure that -2 is a root and (x + 2) is a factor of the given polynomial.  The coefficients of the product of the remaining two factors are {1, -4, 3}.  This trinomial factors easily into {(x -1), (x - 3)}.

Thus, the three factors of the given polynomial are {(x + 2), (x - 1), (x - 3)}