How do you multiply #(3x + 9)(2x + 5)#?

2 Answers
George C.
Aug 30, 2016

#(3x+9)(2x+5)=6x^2+33x+45#

Explanation:

If you find it helpful then you can use the FOIL mnemonic to help collate all the combinations to multiply and add...

#(3x+9)(2x+5) = overbrace(3x*2x)^"First" + overbrace(3x*5)^"Outside"+overbrace(9*2x)^"Inside"+overbrace(9*5)^"Last"#

#color(white)((3x+9)(2x+5)) =6x^2+15x+18x+45#

#color(white)((3x+9)(2x+5)) =6x^2+33x+45#

Tony B
Aug 30, 2016

Another way of showing the same thing:

#6x^2+33x+45#

Explanation:

#color(blue)((3x+9))color(brown)((2x+5))#

Multiply everything inside the right hand side bracket by everything inside the left. Note that the signs follow the value they relate to. So the plus in #+9# follows the 9 and the plus (understood) in #+3x# follows the #3x#
'~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

#color(brown)( color(blue)(3x)(2x+5)" "color(blue)(+9)(2x+5))#

#6x^2+15x" "+18x+45#

#6x^2+33x+45#

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