Finding Vector Paths
How do I find the vector between two points?
- You need to be able to find the vector using a grid
- The grid will be made up of parallelograms or equilateral triangles
- The following grid is made up entirely of parallelograms, with the vectors a and b defined as marked in the diagram:
- Any vector that goes horizontally to the right along a side of a parallelogram will be equal to a
- Any vector that goes up diagonally to the right along a side of a parallelogram will be equal to b
- To find the vector between two points
- Count how many times you need to go horizontally to the right
- This will tell you how many a's are in your answer
- Count how many times you need to go up diagonally to the right
- This will tell you how many b's are in your answer
- Add the a's and b's together
- e.g.
- Count how many times you need to go horizontally to the right
- You will have to put a negative in front of the vector if it goes in the opposite direction
- -a is one length horizontally to the left
- -b is one length down diagonally to the left
- e.g.
Examiner Tip
- Adding and subtracting vectors follows all the same rules as adding and subtracting letters like a and b in algebra (this includes collecting like terms).
- Always look for the easiest path between two points
- Go as far as you can in one direction
- And then use the other direction
Worked example
The following diagram consists of a grid of identical parallelograms.
Vectors and are defined by and .
Write the following vectors in terms of and .
a)
To get from A to E we need to follow vector a four times to the right.
b)
There are many ways to get from G to T. One option is to go from G to Q (b twice), and then from Q to T (a three times).
c)
There are many ways to get from E to K. One option is to go from E to O (b twice), and then from O to K ( -a four times).
also acceptable