2x^2+x-15 дробь x^2+3x

(2х² + х -15) / (х² + 3х) = 2*(х-2,5)(х+3) / х*(х+3) = 2*(х-2,5)/х = (2х-5)/х 

║2х² + х -15 = 0,
║Д = 1² - 4*2-(-15) = 1 + 120 = 121,
║х1 = (-1+11)/2*2 = 10/4 = 2,5,
║х2 = (-1-11)/2*2 = -12/4 = -3,
║значит:
║2х² + х -15 = 2*(х-2,5)(х+3)