Write down its truth value. 1 ! = 0?

Answer 1

1 ! = 1

Answer 2

1!= 1x0=0 

In a sense if you say for example 8! will equal to 8x7x6x5x4x3x2x1x0. 

Answer 3

For all integer values of x > 1,  x! ≠  0;  if x = 1, x! ≠ 0.