Hi, I am working through Hoare Logic problem, I think my invariant is wrong but I cannot think of the good invariant.. please help me with this.

The program:

{n >= 0}

x := 0;

t := 0;

while ( x < n ) do

x := x+1;

t := t+x;

{t = (n^2 + n) / 2}

My invariant was (t = (x^2 +x ) / 2) but it seems that it is wrong