select the product

Question

Select the product of . (3x +7) * (7x - 3)

A. 21x^2 +40x - 21

B. 10x^2 +8x +4

C. 10x^2 +40x - 21

 

D. 21x^2 - 21

 

 

Answer 1

Daniel,

This problem can be solved using a technique known as FOIL.  This technique is based on the distributive property of multiplication where every term in the second expression is multiplied by every term in the first expression.  This is how it will work.

 

First-multiply the first terms together of each expression; here you have 3x(7x) = 21x²

 

Outside-multiply the outside terms together of each expression; 3x(-3) = -9x

 

Inside-multiply the inside terms of each expression; 7(7x) = 49x

 

Last-multiply the last terms of each expression; 7(-3) = -21

 

Now let's combine all these into one expression and we get 21x² - 9x + 49x - 21

 

Next, we combine like terms and we finally get 21x² + 40x - 21

 

I hope this helps.