How do you factor $x^3-3x^2-81x+243$ ?

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Answer 1 · 2016-06-21T13:40:16

$=(x-3)(x+9)(x-9)$

If an expression has 4 more more terms, group them in pairs (or threes) first - making sure there is + sign between the groups.

$(x^3 - 3x^2) + (-81x +243) " look for a common factor"$

$=x^2(x -3) -81(x -3)$

Note that -81 was used as a common factor so the sign in the second bracket changed.
$= (x -3)(x^2-81) " difference of squares"$

$=(x-3)(x+9)(x-9)$

How do you factor x^3-3x^2-81x+243x^3-3x^2-81x+243?