How do you combine #(3k + 4) ( 3k - 5)#?

2 Answers
Jim G.
Feb 20, 2017

#9k^2-3k-20#

Explanation:

Each term in the second bracket must be multiplied by each term in the first bracket as shown below.

#(color(red)(3k+4))(3k-5)#

#=color(red)(3k)(3k-5)color(red)(+4)(3k-5)#

distributing brackets gives.

#=9k^2-15k+12k-20#

collect like terms.

#=9k^2-3k-20#

Barney V.
Feb 20, 2017

#9k^2-3k-20#

Explanation:

#(3k+4)(3k-5)#

#color(white)(........................)3k+4#
#color(white)(........................)ul(3k-5)#
#color(white)(........................)9k^2+12k#
#color(white)(..............................)ul(-15k-20#
#color(white)(.........................)ul(9k^2-3k-20)#

or

#(3k+4)(3k-5)#

#3k xx 3k=color(white)(.....)color(red)(9k^2)#

#4 xx 3k=color(white)(.......)color(red)(12k#

#-5 xx 3k=color(red)(-15k#

#4 xx -5=color(white)(.)-ulcolor(red)(20#

Add the answers together

#:.=color(red)(9k^2+12k-15k-20#

#:.=9k^2-3k-20#

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