Math Is Fun Forum

juantheron

Member

Registered: 2011-10-19

Posts: 312

vector

Let a vector

and

be three vector .

A vector

in the plane of

and

whose projection on

is

is given by

Bob

Administrator

Registered: 2010-06-20

Posts: 10,583

Re: vector

hi juantheron

bobbym: we seem to have a joker here (= coertiolortic).
 
Would you remove him please?

juantheron: I want to check I have understood your question.

I would expect a line to project onto a a plane.

See my first diagram.

If OAB is the plane (shaded yellow) and OC is the third vector,

are you saying that OD, the projection of OC onto the plane has length 1 / √3   ?

And then find the vector OD ?

              [ Does this work with that measurement? ]

OR

second diagram

E lies on OC

D is in the plane.

OE has length 1 /  √3

Bob

Last edited by Bob (2011-12-08 06:44:10)

---

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

juantheron

Member

Registered: 2011-10-19

Posts: 312

Re: vector

actually answer in is given like as

If  a vector

in the plane of 

and 

then it can be express as 

so my question is that why we can not  express

as

because if

and

are in same plane then

are Coplanar. the we can express

as 

So can anyone clear my doubt about that

thank

Last edited by juantheron (2011-12-08 18:03:12)

Bob

Administrator

Registered: 2010-06-20

Posts: 10,583

Re: vector

hi juantheron,

I can clear that up for you.

To move about in a plane you need to know two vectors (not parallel) in the plane.

You can then move anywhere in the plane by going some amount in the direction of one vector followed by an amount in the direction of the other vector. 

ie.

But you also must go from the origin to the plane ( vector OC where C lies in the plane ) so

Diagram below.

For your example, the origin itself may be used for C and so the equation is more simple:

Your alternative:

will not work because you have no parameter for movement in the 'a' direction.  For a plane there must be two parameters to give two degrees of freedom.

So do you still need help with the problem in post #1 ?  I am still unclear what you asking for.

Bob

Last edited by Bob (2011-12-08 20:23:53)

---

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

juantheron

Member

Registered: 2011-10-19

Posts: 312

Re: vector

thanks bob bundy got it

means we can not express in single variable scalar form