x² - 2x - 15 = ( x - 5 ) ( x + 3 )
x² - 10x + 25 = ( x - 5 ) ²
( x - 5 ) ( x + 3 ) / ( x - 5 )² = x + 3 / x - 5
(x - 5)(x + 3)/(x - 5)(x - 5)= simplificam cu (x - 5)= x + 3 / x - 5
