Question 1004550
You can form a square.
Start at (0,0).
First vector (1,0).
Second vector (0,1).
Third vector (-1,0).
Fourth vector (0,-1).
So when you add them all together,
(0,0)+(1,0)+(0,1)+(-1,0)+(0,-1)=(0,0)
So you get back to where you started, you closed the polygon, so the resultant vector is zero.
{{{drawing(300,300,-1,2,-1,2,grid(1),circle(0,0,0.05),circle(1,0,0.05),circle(1,1,0.05),circle(0,1,0.05),blue(line(0,0,1,0)),blue(line(1,0,1,1)),blue(line(1,1,0,1)),blue(line(0,0,0,1)))}}}