# How do you multiply x(x-5)(x-4)?

Apr 14, 2015

$x \left(x - 5\right) \left(x - 4\right)$

Multiply two terms at a time
$\left(x\right) \times \left[\left(x - 5\right) \left(x - 4\right)\right]$

$= \left(x\right) \times \left({x}^{2} - 9 x + 20\right)$

$= {x}^{3} - 9 {x}^{2} + 20 x$

Stop here if you understood the above

Since you are still reading the most likely problem is in multiplying binomials.
There are numerous ways to approach this; perhaps the following will help:

( (xx,,x,+,(-4)), (,-,-,-,-), (x,|,color(blue)(x^2),,color(blue)(-4x)), (+,|,,,), (-5,|,color(blue)(-5x),,color(blue)(+20)), (,-,-,-,-), (,,color(red)(x^2),color(red)(-9x),color(red)(+20)) )

or maybe
$\left(x - 5\right) \times \left(x - 4\right)$
$= \left(x\right) \left(x - 4\right) - \left(5\right) \left(x - 4\right)$
$= \left({x}^{2} - 4 x\right) - \left(5 x - 20\right)$
=(x^2-4x-5x+20
$= {x}^{2} - 9 x + 20$