Question

Даю 45 баллов, нужно подробное решение

Answer 1

x!/(x-3)!=1/20×x!/(x-4)!
(x-3)!(x-2)(x-1)x/(x-3)!=(x-4)!(x-3)(x-2)(x-1)x/20(x-4)1
(x-2)(x-1)x=(x-3)(x-2)(x-1)x/20
(x-3)/20=1
x-3=20
x=23
A из 25 по 2 = 25!/(25-2)!=25!/23!=23!×24×25/23!=24×25=600
C из 36 по 5=36!/(36-5)!5!=36!/31!5!=31!×32×33×34×35×36/31!5!=32×33×34×35×36/1×2×3×4×5=376992
(6!-5!)/5!=(5!×6-5!)/5!=5!(6-1)/5!=5