- is the velocity of the boat relative to the earth. This is in a direction , since that is the direction the boat needs to move.
- is the velocity of the boat relative to the water. This is 10 units (knots) in magnitude. Its direction gives the direction in which the boat will need to steer.
- is the velocity of the water relative to the earth; in other words, the tide or current at 3 knots in a direction .
These vectors are connected by the equation . Notice two things:
- The order of the letters in this equation: they go , just like a displacement vector equation such as
- In the diagram, the arrows on the two vectors that are added (that's ) follow one another around the triangle. The resultant, or sum, of these two vectors is the third vector .
So that's how the diagram is drawn. You'll need to use the Sine Rule to calculate the angle between and the North, to give you the bearing that the boat must steer. Can you complete this now?