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

1 Answer
Alan P.
Apr 14, 2015

#x(x-5)(x-4)#

Multiply two terms at a time
#(x) xx [(x-5)(x-4)]#

#= (x) xx (x^2-9x+20)#

#=x^3-9x^2+20x#

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
#(x-5)xx(x-4)#
#= (x)(x-4) - (5)(x-4)#
#=(x^2-4x) - (5x-20)#
#=(x^2-4x-5x+20#
#=x^2-9x+20#

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