# c4 vectors (again)

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hi, i'm really struggling on the last part (f) on question 8 and the guy from YouTube who explains it does an awful job can anyone help please ?

http://pmt.physicsandmathstutor.com/...%20Edexcel.pdf

http://pmt.physicsandmathstutor.com/...%20Edexcel.pdf

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(Original post by

hi, i'm really struggling on the last part (f) on question 8 and the guy from YouTube who explains it does an awful job can anyone help please ?

http://pmt.physicsandmathstutor.com/...%20Edexcel.pdf

**Virolite**)hi, i'm really struggling on the last part (f) on question 8 and the guy from YouTube who explains it does an awful job can anyone help please ?

http://pmt.physicsandmathstutor.com/...%20Edexcel.pdf

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maybe because one unit vector on line L2 is equal to route54 thus we need to make it route24 so we multiply by 2/3 so then does this mean U = 2/3 and if so why

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(Original post by

maybe because one unit vector on line L2 is equal to route54 thus we need to make it route24 so we multiply by 2/3 so then does this mean U = 2/3 and if so why

**Virolite**)maybe because one unit vector on line L2 is equal to route54 thus we need to make it route24 so we multiply by 2/3 so then does this mean U = 2/3 and if so why

will equal +/- 2/3, as appropriate for B1, B2.

The direction vector for l2 has length root(54), so we need to divide it by root(54) to get a unit vector (a vector of length 1) in the same direction as the direction vector for l2.

Then since we need the vector from X along l2, to have length root(24), we multiply by root(24).

**Edit:**Correct typo 45 to 54

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(Original post by

Essentially, you have that right.

will equal +/- 2/3, as appropriate for B1, B2.

The direction vector for l2 has length root(54), so we need to divide it by root(45) to get a unit vector (a vector of length 1) in the same direction as the direction vector for l2.

Then since we need the vector from X along l2, to have length root(24), we multiply by root(24).

**ghostwalker**)Essentially, you have that right.

will equal +/- 2/3, as appropriate for B1, B2.

The direction vector for l2 has length root(54), so we need to divide it by root(45) to get a unit vector (a vector of length 1) in the same direction as the direction vector for l2.

Then since we need the vector from X along l2, to have length root(24), we multiply by root(24).

why does dividing the unit vector by root(45) give a unit vector of size 1, not sure where the value of root(45) comes from?

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thanks for the reply

why does dividing the unit vector by root(45) give a unit vector of size 1, not sure where the value of root(45) comes from?

**Virolite**)thanks for the reply

why does dividing the unit vector by root(45) give a unit vector of size 1, not sure where the value of root(45) comes from?

First off, lets get the terminology correct.

A unit vector is a vector of length 1.

in the lines l1, l2, the vectors multiplied by mu and lambda are direction vectors (they indicate the direction of the lines). They are not unit vectors.

The magnitude of a vector, ai+bj+ck is , so if we divide the vector by that to start with, then the magnitude of the resulting vector is 1. Work it through yourself, to check.

This should also indicate to you where the root(54) comes from.

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(Original post by

You mean root(54), not 45.

First off, lets get the terminology correct.

A unit vector is a vector of length 1.

in the lines l1, l2, the vectors multiplied by mu and lambda are direction vectors (they indicate the direction of the lines). They are not unit vectors.

The magnitude of a vector, ai+bj+ck is , so if we divide the vector by that to start with, then the magnitude of the resulting vector is 1. Work it through yourself, to check.

This should also indicate to you where the root(54) comes from.

**ghostwalker**)You mean root(54), not 45.

First off, lets get the terminology correct.

A unit vector is a vector of length 1.

in the lines l1, l2, the vectors multiplied by mu and lambda are direction vectors (they indicate the direction of the lines). They are not unit vectors.

The magnitude of a vector, ai+bj+ck is , so if we divide the vector by that to start with, then the magnitude of the resulting vector is 1. Work it through yourself, to check.

This should also indicate to you where the root(54) comes from.

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ohh brilliant thanks, the root(45) i was referring to was what you mentioned in your first post "The direction vector for l2 has length root(54), so we need to divide it by root(45) to get a unit vector (a vector o" was that juts a typo i guess?

**Virolite**)ohh brilliant thanks, the root(45) i was referring to was what you mentioned in your first post "The direction vector for l2 has length root(54), so we need to divide it by root(45) to get a unit vector (a vector o" was that juts a typo i guess?

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(Original post by

Yep, sorry. Typo on my part - corrected now.

**ghostwalker**)Yep, sorry. Typo on my part - corrected now.

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