How do you evaluate #(2.5a - 1.8) ( 5a + 8)#?

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Answer 1 · 2017-11-21T19:42:22

#12.5a^2 + 11a - 14.4#

#(2.5a - 1.8)(5a + 8)#

If you have heard of solving this the Rainbow way, FOIL, box method, etc, that is how you solve this problem.

#2.5a * 5a = 12.5a^2#

#2.5a * 8 = 20a#

#-1.8 * 5a = -9a#

#-1.8 * 8 = -14.4#

Now, we put all of these together:
#12.5a^2 + 20a - 9a - 14.4#

We see that #20a# and #-9a# are 'like-terms' because they both have one #a#. This means that we can do #20a-9a = 11a#.

So our final expression is #12.5a^2 + 11a - 14.4#

Answer 2 · 2017-11-21T19:55:30

#(2.5a-1.8)(5a+8)=color(blue)(12.5a^2+11a-14.4#

Simplify:

#(2.5a-1.8)(5a+8)#

Expand using the FOIL method.

(a+b)(c+d)=ac(First)+ad(Outer)+bc(Inner)+bd(Last)

#(2.5a-1.8)(5a+8)=(2.5a*5a)+(2.5a*8)+(-1.8*5a)+(-1.8*8)#

Simplify the parentheses.

#(2.5a-1.8)(5a+8)=12.5a^2+20a+ -9a+ -14.4#

Gather like terms.

#(2.5a-1.8)(5a+8)=12.5a^2+(20a-9a)-14.4#

Simplify.

#(2.5a-1.8)(5a+8)=12.5a^2+11a-14.4#