about groups?

Question

for any integer n>2 show that there are at least 2 elements in U-n
that satesfies
x^2=1
U-n"is agroup under multiblication modulu n;

Answer 1

1 and n-1 will always work.

1^2 = 1 (mod n), and
(n-1)^2 (mod n) = n^2-2n+1 = 1 (mod n).

Answer 2

1 and -1(= n-1) always satisfy x² = 1(mod n)