Answer:
Step-by-step explanation:
r² - 12r - 28 = 0
r² - (14 - 2)r - 28 = 0
r² - 14r + 2r - 28 = 0
r ( r - 14 ) + 2 ( r - 14 ) = 0
( r - 14) ( r + 2 ) = 0
Either
r - 14 = 0
r = 14
or
r + 2 = 0
r = -2
therefore r = - 2 or 14
