Ответы и объяснения

2011-11-15T12:19:00+04:00

11!=11*10!

11!-(1*1!+2*2!+3*3!+...+10*10!)=11*10!-10*10!-(1*1!+...+9*9!)=

10!-(1*1!+...+9*9!)= 10*9!-9*9!-(1*1!+...+8*8!)=

9!-(1*1!+...+8*8!)=  

... 

2!-(1*1!) = 2-1 = 1