Which statement explains the relationship of sides BA and B'A' after rectangle BADC has been rotated 90° counterclockwise about the origin?

Side B'A' has a slope of 1 and is parallel to side BA.
Side B'A' has a slope of −1 and is parallel to side BA.
Side B'A' has a slope of 1 and is perpendicular to side BA.
Side B'A' has a slope of −1 and is perpendicular to side BA.

Since the resultant force is exactly the sum of the two component forces, the angle between the forces (i.e. if they were placed tail to tail) is 0. In other words, the two component forces are acting in exactly the same direction. If the angle was 180, the forces would be acting in opposite directions (the resultant force would be the difference between them, not the sum), and if the angle was anything in between 0 and 180, the resultant force would be less than 5F.