Adding vectors

Here you will learn about adding vectors, including what it is and how to do it.

Students will first learn about adding vectors as part of the number system in high school.

What is adding vectors?

Adding vectors is adding one vector to another vector. This is sometimes known as a vector sum.

As vectors can be located anywhere in a space, the start of the vector is called the tail, and the end of the vector is called the head. The direction of the vector is therefore from the tail to the head and is indicated using an arrow through the middle of the vector.

Here, the arrow of vector \vec{v}=\langle{3,2}\rangle points from the tail to the head of the vector.

Let’s look at some examples of vectors.

For the addition of vectors, \vec{a}+\vec{b}, place the tail of vector \vec{b} onto the head of vector \vec{a}.

Adding the vectors forms the new vector \vec{a}+\vec{b}. This is drawn as a straight line from the tail of \vec{a} to the head of \vec{b}.

Now you can identify the components of the new vector. Notice they form the base and height of a right triangle, in which the vector is the hypotenuse.

Here, the horizontal x component of the vector \vec{a}+\vec{b} is 4 right and the vertical y component is 6 up. So \vec{a}+\vec{b}=\langle{4,6}\rangle.

Though it can be helpful, when finding a vector sum you do not have to draw a diagram. You can just add the vector components. First, add the x components (first numbers) and then add the y components (second numbers).

The new vector that results from adding two given vectors is known as the resultant vector.

The addition of vectors is commutative which means that the order in which you add the vectors is not important. In other words we will get the same result if you add the second vector to the first vector.

The diagram is a parallelogram. The resultant vector is the diagonal of the parallelogram.

Note: This page covers only 2 -dimensional vectors.

What is adding vectors?

Common Core State Standards

How does this relate to high school math?

• The Number System (HSN.VM.B.4a)
  Add vectors end-to-end, component-wise, and by the parallelogram rule. Understand that the magnitude of a sum of two vectors is typically not the sum of the magnitudes.

• The Number System (HSN.VM.B.4b)
  Given two vectors in magnitude and direction form, determine the magnitude and direction of their sum.

How to add vectors

In order to add vectors:

1. Add the \textbf{x} components.
2. Add the \textbf{y} components.
3. Write the resultant vector.

Adding vectors examples

Example 1: add vectors graphically

Add the given vectors, \langle{2,4}\rangle+\langle{5,1}\rangle, shown on the coordinate plate.

Notice the direction of the vectors is positive.

1. Add the \textbf{x} components.

Connect the tail of vector \vec{a} to the head of vector \vec{b} to show the resultant vector \vec{a}+\vec{b}.

Look at the horizontal change from the tail of the first vector to the head of the second vector.

The horizontal x component is 7 right, or 7.

2Add the \textbf{y} components.

Look at the vertical change from the tail of the first vector to the head of the second vector.

The vertical y component is 5 up, or 5.

3Write the resultant vector.

Example 2: add vectors graphically

Write the resultant vector \vec{a}+\vec{b} in the form \langle{x,y}\rangle.

Add the \textbf{x} components.

Draw a straight line connecting the tail of \vec{a} to the head of \vec{b} and draw an arrow to show the direction of the vector \vec{a}+\vec{b}.

Look at the horizontal change from the tail of the first vector to the head of the second vector.

Add the \textbf{y} components.

Look at the vertical change from the tail of the first vector to the head of the second vector.

Example 3: add three vectors

Add the given vectors: \langle{8,2}\rangle+\langle{7,1}\rangle+\langle{3,0}\rangle

Example 4: add vectors including negative numbers

Add the given vectors: \langle{- \, 5,- \, 2}\rangle+\langle{2,- \, 4}\rangle

Example 5: add vectors including a scalar

Let \vec{a}=\langle{7,3}\rangle and \vec{b}=\langle{- \, 3,- \, 4}\rangle. Calculate 2\vec{a}+\vec{b} writing your answer in the component form of the vector.

Example 6: add vectors including 0

Let \vec{a}=\langle{- \, 3,- \, 1}\rangle,~\vec{b}=\langle{- \, 2,4}\rangle and \vec{c}=\langle{5,- \, 3}\rangle. Find \vec{a}+\vec{b}+\vec{c}. Write your answer in the component form.

Teaching tips for adding vectors

• Instead of jumping to the rule, let students explore adding vectors using the head-to-tail method on coordinate system graphs. This will help them understand why the rule for adding vectors work and in turn help them have a deeper understanding of vectors.

• Make sure that students understand the vocabulary for the components of a vector. Terms such as tail (starting point), head (end point), magnitude and direction should be clearly defined for students.

Easy mistakes to make

• Incorrectly adding negative integers
  Mistakes can easily be made when adding a positive number and a negative number. Make sure that students’ negative numbers skills are well practiced before teaching vectors. For example, 3+(- \, 4)=3-4=- \, 1

• Corresponding components with the wrong axes
  The horizontal components are related to the x -axis and the vertical components y -axis. Show students how this connects to their knowledge of the coordinate grid.

• Confusing scalars, vectors and matrices
  Since this is an introductory topic, students may easily confuse terms. Clearly give examples of each and correct students when they use these terms incorrectly.

Related vectors lessons

• Component form of a vector
• Subtracting vectors
• Vector multiplication
• Vector practice problems

The next lessons are

• Lines
• Angles
• Angles in parallel lines
• Trigonometry

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