30 * А [4,х-2]= А [5,х]
30 * (х-2)! / (х-2-4)! = х! / (х-5)!
30 * (х-2)! / (х-2-4)! = (х-2)! * (х-1)х / (х-5)!
30 / (х-6)! = (х-1)х / (х-6)! (х-5)
30 = (х-1)х / (х-5)
30(х-5) = х (х-1)
х² - х = 30х - 150
х² - 31х + 150 = 0
Д = (-31)² - 4*1*150 = 961 - 600 = 361 = (±19)²
Х1 = (31 + 19)/2 = 20
Х2 = (31 - 19)/2 = 6