Confirm time complexity

#1

int a = 0;
for (i = 0; i < N; i++) {
for (j = N; j > i; j–) {
a = a + i + j;
}
}

would be o(N)

as n+(n-1)+(n-2)…
???

#2

No, as n+(n-1)+(n-2)…
will compute to n(n-1)/2
which is o(n^2)

#3

oh yeah!!, done by mistake.