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

1 Answer
Jun 21, 2016

Answer:

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

Explanation:

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)#