5n² - 8n - 21 → (5)(- 21) = -105 (find 2 numbers whose product is 105 and sum is -8)
= 5n² - 15n + 7n - 21
= 5n(n - 3) + 7(n - 3)
= (5n + 7)(n - 3)
*****************************************************
6n² + 53n - 79 → (6)( -79) = -474 (find 2 numbers whose product is -474 and sum is 53) DOES NOT EXIST! only factors are: (1, 474) (2, 237) (3, 158) (6, 79)
= Prime
*******************************************************
4n² - 25 (this is the difference of two squares)
= √(4n²) +/- √(25)
= 2n +/- 5
= (2n + 5)(2n - 5)
