How do you multiply #(-20x -12)(-19x -15)#?

1 Answer
May 9, 2018

Answer:

#380x^2+ 528x + 180#

Explanation:

#color(red)((-20x - 12)(-19x - 15))#

doing this is like doing #2(x + 4)#
you times the number outside the brackets, #color(blue)(2)#, with everything inside the brackets, #color(blue)((x + 4))#
#2 xx x = color(blue)(2x#
#2 xx 4 = color(blue)8#
#color(blue)(2x + 8)#
#2(x + 4)# becomes #2x + 8#

So, with #color(red)((-20x - 12)(-19x - 15))#
You times these together first...
#(color(red)(-20x) - 12)(color(red)(-19x - 15))#
like...
#-20x xx -19x = color(blue)(380x^2#
#-20x xx -15 = color(blue)(300x#

then you do the same with...
#(-20x color(red)(-12))(color(red)(-19x - 15))#
like...
#-12 xx -19x = color(blue)(228x#
#-12 xx -15 = color(blue)(180)#

When you put everything together, you get something like this
#color(blue)(380x^2 + 300x + 228x + 180#
And when you solve that...

#380x^2 color(blue)(+ 300x + 228x) + 180#
#380x^2 color(blue)(+ 528x) + 180#