Question

Choose the correct product of (7x − 3)(7x + 3). 49x2 + 9 49x2 − 42x + 9 49x2 − 9 49x2 + 42x + 9

Answer 1

Using FOIL (First Outside; Inside, Last), we find our product.

(7x - 3)(7x + 3) // Given
7x * (7x + 3) // First Outside
49x^2 + 21x // Distribute (remember this)
-3 * (7x + 3) // Inside Last
-21x - 9 // Distribute (remember this)
49x^2 + 21x - 21x - 9 // Add both answers (the one from Outside and the one from Inside)
49x^2 - 9 // Simplify. This is your answer

You can do this, or you can remember that this is a factor for a difference of squares, where

a^2 - b^2 = (a + b)(a - b)

Plug in “7x” for a, “3” for b