Question

РЕШИТЕ УРАВНЕНИЕ (Х+1)!/20=(х-1)!

Answer 1

$frac{(x+1)!}{20} = (x-1)!; x in mathbb{N} \ n! = n(n-1)! \ frac{x(x+1)(x-1)!}{20} = (x-1)! |:(x-1)! \ frac{x(x+1)}{20} = 1 | 20 \ x(x+1) = 20 \ x(x+1) = 4*5 \ x = 4$