Select the difference of (3x +7) * (7x - 3)

Question

Select the difference of (3x +7) * (7x - 3)

 

A. 21x^2 +40x -21

 

B. 10x^2 +8x +4

 

C. 10x^2 +40x - 21

 

D. 21x^2 - 21

 

Which is it?

Answer 1

Not sure about the wording "difference", but if you are to multiple these two:

 

FOIL, multiply First, Outer, Inner, Last

 

First terms: 3x and 7x

Outer terms: 3x and -3

Inner terms: 7 and 7x

Last terms: 7 and -3

 

You get 21x² -9x +49x -21

Combine like terms, and 21x²+ 40x -21 is your answer