Infinite Factorials

x ! x ! x ! . . . = 1 \LARGE { x! }^{ { x! }^{ { x! }^{ { }^{.^{.^{.}}} } } } =\ 1

Given that x ( > 0 ) x\, (>0) satisfies the infinitely nested function above, find x x .


The answer is 1.

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7 solutions

Mateus Gomes
Feb 11, 2016

x ! x ! x ! = 1 \Large{ x! }^{\color{#D61F06}{{ x! }^{ { x! }^{ \dots } } }}=\color{#D61F06}{1} ( x ! ) 1 = 1 \Large({ x! })^{\color{#D61F06}{1}}=\color{#D61F06}{1} x ! = 1 ( x > 0 ) ~~~~~~~~~~~~~~~~\large\color{#3D99F6}{\boxed{ x!=1}}~~(x>0)

Roy Satyam
Nov 26, 2017

INDIANS ARE BEST MATHEMATICIAN

. .
Feb 23, 2021

1 ! 1 ! 1 ! = 1 x = 0 , x = 1 { { 1! ^ { 1! } } ^ { 1! } }^ { \cdots } = 1 \Rightarrow x = 0, x = 1 , but x > 0 x > 0 , so the answer is 1 \boxed { 1 } .

Gia Hoàng Phạm
Aug 20, 2018

x ! x ! x ! = 1 y = x ! y = 1 y = 1 = x ! 1 = x ! x < 0 , x = 0 , 1 x = 1 x!^{x!^{x!^{\dots}}}=1 \implies y=x!^y=1 \implies y=1=x! \implies 1=x! \implies x<0,x=0,1 \implies x=1

Abhishek Mittal
Nov 15, 2017

here we know that 1! is the only term which is greater than zero and having its value 1 .

No number except 1 works in this formula since no factorial value equals 0, so the value of the raised factorial powers has to be 1.

Keshav Ramesh
Mar 4, 2017

No factorial value equals 0 0 , so the value of the raised factorial powers has to be 1 1 . The only number to the 1 1 power which equals 1 1 is 1 1 , therefore giving us our answer of 1 1 .

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