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