Main content

## Algebra (all content)

### Course: Algebra (all content) > Unit 19

Lesson 5: Combined vector operations# Combined vector operations

Watch Sal find new vector 3u + 1/5w when u = (2, -1) and w = (-5, 5).

## Want to join the conversation?

- My answer includes a square root. How do I indicate a square root using characters from the keyboard?(9 votes)
- You can just type in "sqrt" in the answer box and you should get a square root. Alternatively, if you hover the mouse above the answer box you should get several symbols below, one of which is the square root. Click on it.(22 votes)

- Can you add scalars to vectors? Can you multiply vectors by other vectors?(3 votes)
- You cannot add scalar and vector, even if they have the same units (e.g. distance and displacement). Vector multiplication can be done in two ways : Dot product or Cross product.(12 votes)

- if A=[1,4,3] and B=[2,-1,5] then the midpoint M of vector AB..........?(3 votes)
- the midpoint is (1.5,1.5,4)

you just add the co-ordinates in each of the axis and then divide by two. like (1+2)/2,(4+-1)/2,(3+5)/2(9 votes)

- How do we add vectors on graph paper example(3 votes)
- there are previous videos in this section that refer to graphically adding vectors. we can add them by making a triangle. When we add these two vectors we get a resultant vector which is the answer.(4 votes)

- Lets say that vector w is (3,5). so would vector w+1 be (4,6)?(2 votes)
- Can vectors be divided ?(3 votes)
- A vector can be divided by a scalar but a vector cannot be divided by another

However magnitude of vectors can be divided(2 votes)

- how do I find the Magnitude?(1 vote)
- To find the magnitude of a vector ai+bj, you can use Pythagorean Theorem. The magnitude would be the square root of (a^2+b^2).

Hope this helps! If you have any further questions, please ask! :)(3 votes)

- PLS! I need the same exercise but between 3u and 1/5w we have multiplication!(1 vote)
- There are two kinds of vector multiplication. I would look in the section that discusses either dot product multiplication (produces a scalar answer) or cross product multiplication (produces a vector orthogonal to the original two input vectors). This is just a beginners intro to vector math.(1 vote)

- where did the 3 come from or was it apart of the original problem?(1 vote)
- The 3 is just part of the problem.

We have the vectors 𝒖 and 𝒗,

and we want to find the vector 3𝒖 + (1∕5)𝒗.(1 vote)

- What about when the vectors are being subtracted?(1 vote)
- Subtracting vectors works like vector addition, only you subtract instead of adding.(1 vote)

## Video transcript

- [Voiceover] So what we have
right over here, we have the vector U and we've defined it
by giving its X & Y components it's a two-dimensional vector,
and we have the vector W. And we've graphed them, the vector U, its X component is two, its
Y component is negative one. So if we put its initial point
at the origin, the terminal point, or its head, will
be at the point two, comma, negative one, which is right over there. And for vector W, it's
negative five, comma, five. So its X component is negative five. So if we start at the origin
we would move five to the left. And its Y component is
positive five, so we would move five up then to
get to the head of the vector, or to get to the terminal point. Now given these two vectors,
what we wanna do is evaluate what three times the
vector U, plus one fifth times the vector W is, and I encourage you to pause the video and to give a go at it. Well three and one fifth are scalers. They are going to scale these
vectors and we're gonna see them, see that happen visually. So we're gonna scale up
vector U by three, we're gonna scale down vector W, we're
gonna multiply it by one fifth, and then we're gonna add
the resulting vectors. So let's do that. So when we scale vector U by
three, we could just do this as three times vector U, we
know is a vector two, comma, negative one, and so that's
going to be, we could write it this way, so let me write
the two, let me write the negative one, that's
going to be three times two, for the new X component
once we scale it up. And three times negative
one for the new Y component, and of course that's going
to be, result in the vector three times two, our new X
component is six, and our new Y component is going to be negative three. And so let's plot that. So everything I've done just now is that part of the expression,
that part of the expression. So the vector six, comma, negative three, if we start it at the origin,
we're going to move, let's see we're going to move one,
two, three, four, five, six in the X direction and negative
three in the Y direction. So one, two, three, one, two, three, so we would get right about there. So there you have it, this
is the vector three U. And we're at one, two,
three, four, five, six in the X direction, or six to the right, and then we went down
three, one, two, three, in the Y direction, and
notice, it's in the exact same direction as vector U, it just
has three times the magnitude that's vector U, that would be two U. And then we get to three U,
three times the magnitude. Alright, now let's figure out
what one fifth times W is. Let's see one fifth times W,
well let me just write this, it's gonna be plus one fifth,
W is the vector, is the vector negative five, comma, five,
and so this is gonna be plus, so that's gonna be, let me
write the components down. So it's gonna be plus one fifth, times, one fifth times negative five, and the Y component is gonna
be one fifth times five, and so that's gonna be plus,
whoops I wrote one half, my brains not working properly, one fifth times negative five,
and one fifth times five. And so, this part right over
here is going to be one fifth times negative five, is negative one, and one fifth times five is positive one. And so this new vector, one fifth W, is gonna be W scaled down. And so it's negative one,
comma, one if we start it at the origin, so
negative one, comma, one. We'd get right over there, and notice, it's going in the same direction as W, it's just one fifth, it's
just one fifth as long. And now we just wanna
add these two vectors. So if we add them by just
looking at its components, the resulting vector,
the resulting vector, let me do this in a new color
that I have not used yet, so the resulting vector, we're
gonna add the corresponding X components, so it's going to be six plus negative one, six plus negative one, and
the resulting Y component is going to be negative three plus one. Negative three plus one. And so the resulting vector
is going to be equal to five, comma, negative two. And we can also see that visually. If we start with this blue
vector, three times the vector U, and we were to add the
green vector, one fifth W, well we were to add that we
would just start at the head of three U, then we're gonna
add negative one, comma, one, so we're gonna move one
to the left and one up, we're gonna get right over there. So let me see if I can draw that. So, just gonna do a
little head to tail method right over here, so the
head of the first vector is gonna be where the tail of the next vector starts, that we're adding. And so the resulting vector
is going to be, if we started at the tail of the first
vector, three U right over here, or at the origin, and then
we bring it to the head of the second vector, we get, once again, the vector five, comma, negative two. Its X component is five, we're
gonna move five to the right, and we move two down.