# Math Is Fun Forum

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## #1 2016-09-16 18:42:33

Zeeshan 01
Member
Registered: 2016-07-22
Posts: 746

### Vector

Question :How to write vector PQ in the form xī+yj
Where P =(2,3) and q(-4,7) plese help thx

Malik

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## #2 2016-09-16 19:54:49

Bob
Registered: 2010-06-20
Posts: 9,299

### Re: Vector

hi Zeeshan 01

You have OP = 2i + 3j and OQ = -4i + 7j .

PQ = PO + OQ = -2i - 3j  -4i + 7j = -6i + 4j

If you fraw a coordinate diagram and plot the points you'll see what 'i' and 'j' is needed to travel from P to Q.

Bob

Children are not defined by school ...........The Fonz
You cannot teach a man anything;  you can only help him find it within himself..........Galileo Galilei
Sometimes I deliberately make mistakes, just to test you!  …………….Bob

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## #3 2016-09-17 00:53:04

Zeeshan 01
Member
Registered: 2016-07-22
Posts: 746

### Re: Vector

In O how come I and j and what is I and j thx for help

Malik

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## #4 2016-09-17 03:11:09

Bob
Registered: 2010-06-20
Posts: 9,299

### Re: Vector

Vectors and coordinates are part of the same topic.  O = (0,0) is the origin and P = (2,3) is just another way of saying vector OP = 2i and 3j.

i is the unit vector in the x direction and j is the unit vector in the y direction.  So when you describe a point as (2,3) what you are really saying is that, starting from the origin, you need to go 2 in the x direction (or 2i) and 3 in the y direction (or 3j) to reach P.

Bob

ps.  My computer keeps changing i to I. This is because I have got certain auto-adjust spelling corrections set up.  If you go back to the I and change it back to i the auto-adjust usually gives up.

Bob

Children are not defined by school ...........The Fonz
You cannot teach a man anything;  you can only help him find it within himself..........Galileo Galilei
Sometimes I deliberately make mistakes, just to test you!  …………….Bob

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## #5 2016-09-17 03:53:46

Zeeshan 01
Member
Registered: 2016-07-22
Posts: 746

Hahah no worry

Malik

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## #6 2016-09-17 21:33:50

Zeeshan 01
Member
Registered: 2016-07-22
Posts: 746

### Re: Vector

So when there is Xi and yj so what it's saying???

Malik

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## #7 2016-09-18 01:55:27

Bob
Registered: 2010-06-20
Posts: 9,299

### Re: Vector

hi Zeeshan 01,

I am not sure what you are asking.  So I will go back to basics and explain why vectors and coordinates are part of the same topic.

Maths theorists usually start with vector spaces.  To keep it simple, let's make a 2 dimensional vector space.

The vectors a and b here are not parallel so you may use them as a basis for the space.  That means that any other vector can be written as a linear combination of a and b.

To demonstrate this, I've drawn another vector c.  It could be any vector so I just choose one at random.

I've then made two dotted lines.  The first goes through O and A and extends as far as necessary in both directions.  The second is parallel to OB but goes through C.

Because OA and OB are not parallel, the dotted lines must cross somewhere.  I have called that point P.  If you count squares you will see that

You can use this method to make any vector a linear combination of a and b.

a and b are said to form a basis for the space.  Nothing special about a and b either.  I just drew any two non parallel lines through (0,0).

One special basis is the one made by the unit vectors

and

If they are used as the basis then

And then we define the coordinates of C to be those two numbers and write C = (-6,6)

Bob

Children are not defined by school ...........The Fonz
You cannot teach a man anything;  you can only help him find it within himself..........Galileo Galilei
Sometimes I deliberately make mistakes, just to test you!  …………….Bob

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## #8 2016-09-18 03:27:58

Zeeshan 01
Member
Registered: 2016-07-22
Posts: 746

?

Malik

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## #9 2016-09-18 04:18:17

Bob
Registered: 2010-06-20
Posts: 9,299

### Re: Vector

hi Zeeshan 01

I want to help but I need you to say more than ???  What don't you understand?  Or give an example of what you do understand.

Bob

Children are not defined by school ...........The Fonz
You cannot teach a man anything;  you can only help him find it within himself..........Galileo Galilei
Sometimes I deliberately make mistakes, just to test you!  …………….Bob

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## #10 2016-09-20 01:23:16

Zeeshan 01
Member
Registered: 2016-07-22
Posts: 746

### Re: Vector

Can u tell what you describe above thx

Malik

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## #11 2016-09-20 23:17:32

Bob
Registered: 2010-06-20
Posts: 9,299

### Re: Vector

I thought that was what I did.  Please say exactly where you are confused.

Bob

Children are not defined by school ...........The Fonz
You cannot teach a man anything;  you can only help him find it within himself..........Galileo Galilei
Sometimes I deliberately make mistakes, just to test you!  …………….Bob

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## #12 2016-09-21 00:53:11

Zeeshan 01
Member
Registered: 2016-07-22
Posts: 746

### Re: Vector

Means vector work on space....
space mean distance or other space where planet exist

Malik

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## #13 2016-09-21 00:54:21

Zeeshan 01
Member
Registered: 2016-07-22
Posts: 746

### Re: Vector

Which space does it means???

Malik

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## #14 2016-09-21 03:31:51

Bob
Registered: 2010-06-20
Posts: 9,299

### Re: Vector

Nothing to do with space, the final frontier.

A vector space could just be all the points in plane.  We say that is a two dimensional space.

It could be three dimensional, it which case you would need vectors with three components in the x, y and z directions.

It could also have four, five, .... n dimensions, but you probably won't need to worry about those.

I kept it simple in my example by sticking to two dimensions.

Hope that explains that part.  Next question?

Bob

Children are not defined by school ...........The Fonz
You cannot teach a man anything;  you can only help him find it within himself..........Galileo Galilei
Sometimes I deliberately make mistakes, just to test you!  …………….Bob

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## #15 2016-09-21 19:12:32

Zeeshan 01
Member
Registered: 2016-07-22
Posts: 746

### Re: Vector

I your above explaination you say I and j tell what to go on x axis and y axis eg 6i and 7j used to tell  go to 6 in xaxis and 7 in y axis so when there is Xi and yj what this tell???

Malik

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## #16 2016-09-21 19:29:40

Bob
Registered: 2010-06-20
Posts: 9,299

### Re: Vector

If you had xi and yj,  this would be a vector that starts at (0,0) and goes 'x' across and 'y' up.  So it would be the vector way to show a general point which would be the same as (x,y) in coordinate form.

Bob

Children are not defined by school ...........The Fonz
You cannot teach a man anything;  you can only help him find it within himself..........Galileo Galilei
Sometimes I deliberately make mistakes, just to test you!  …………….Bob

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