What is "Triangle rule of addition" ?

What is "triangle rule of addition" ?

If a particle is given two velocities simultaneously  its resultant effect velocity is different from the two velocities and is obtained by using a special rule I.e "Triangle rule of addition " 

Suppose a small ball is moving inside a long tube at a speed of 3 m/s and the tube itself is moving in the room at a speed of 4 m/s along a direction perpendicular to its length. In which direction and how fast is the ball moving as seen from the room ?

Above figure shows position of tube and the ball. By pythagorean we conclude that resultant velocity is 5 m/s. 

General rule for finding the resultant of two velocities may stated as follows :-

Draw a line AB representing first velocity with B as the head. Draw another line BC representing second velocity with its tail B coinciding with the head of the first line. The line AC with A as the tail and C as the head represents the resultant velocity. Above figure shows the construction 

        The resultant is also called the sum of the two velocities. We have added the two velocities AB and BC and have obtained  the sum AC. This rule of addition is called the "Triangle rule of addition ".

Thanks for reading. I really appreciate your time.🔝🔥🔥🔥