Question

Este adevarat ca  $\sqrt{1+3+5 + ... + 2007}$ apartine lui Q ?

Answer 1

1+3+5+...+2007=
1+3+5+...+2n-1=n*n
2007=2n-1
2008=2n
n=2008:2
n=1004
suma=1004*1004=1004^2
radical din 1004^2=1004
Deci da, 1004 apartine Q