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3 votes
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10 points
(5x - 4)(x + 5)

O 5x²+21x-20
O4x²-17x+4
O 10x²+20x+10
O 10x²-10

1 Answer

3 votes

Answer:

First choice: 5x²+21x-20

Explanation:

This is easy to answer if you realize that there is only one way an x² term can appear in the result and that is by the multiplication of 5x and x which results in 5x².

The only choice which has 5x² as a term is the first: 5x²+21x-20

However, it is important to know the FOIL method to multiply two terms together

FOIL stands for First Outer Inner Last and is a technique for multiplying two terms of the form (a+b) and (c+d)

In (a + b) (c + d),

First terms are a and c so their product is ac

Outer terms are a and d so their product is ad

Inner terms are b and c with product bc

Last terms are b and d with product bd

The result is the sum of all these terms

Let's take (5x - 4)(x + 5)
F: 5x·x = 5x²

O: 5x · 5 = 25x

I: -4 ·x = -4x

L: -4·5 = -20

Adding up these individual terms we get

5x² +25x - 4x - 20 = 5x²+21x-20

So first choice is the correct answer

User Damien Debin
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