Verified answer

task/30400470    A_n ⁵ = 18*A_(n₋2) ⁴

решение    A_n ⁵ = 18*A_(n₋2) ⁴ ⇔

n(n-1)(n-2)(n-3)(n-4)=18*(n-2)(n-3)(n-4)(n-5) || : (n-2)(n-3)(n-4) ≠ 0

n(n-1) = 18(n-5) ⇔n² -19n +90 =0 ⇔ [ n = 9 , n = 10 .