# Vectors Watch

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How do you do this?

2. Given that

Thanks

2. Given that

**a**= 2 +**j**and**b**=**i**+ 3**j**find a, (cant do the symbol on comp looks like a lambda), if**a + lambda b**is parallel to the vector**i**Thanks

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#2

(Original post by

How do you do this?

2. Given that

Thanks

**DOJO**)How do you do this?

2. Given that

**a**= 2 +**j**and**b**=**i**+ 3**j**find a, (cant do the symbol on comp looks like a lambda), if**a + lambda b**is parallel to the vector**i**Thanks

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(Original post by

Sorry why a = 2 + j? You mean 2i + j, or 2j?

**BCHL85**)Sorry why a = 2 + j? You mean 2i + j, or 2j?

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#4

Ok, a + l.b = ki

2i + j + li + 3lj = ki

(2+l)i + (1+3l)j = ki

So 1 + 3l = 0 -> l = -1/3

And you want to find lamda (l), don't you?

2i + j + li + 3lj = ki

(2+l)i + (1+3l)j = ki

So 1 + 3l = 0 -> l = -1/3

And you want to find lamda (l), don't you?

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(Original post by

Ok, a + l.b = ki

2i + j + li + 3lj = ki

(2+l)i + (1+3l)j = ki

So 1 + 3l = 0 -> l = -1/3

And you want to find lamda (l), don't you?

**BCHL85**)Ok, a + l.b = ki

2i + j + li + 3lj = ki

(2+l)i + (1+3l)j = ki

So 1 + 3l = 0 -> l = -1/3

And you want to find lamda (l), don't you?

Your answer of -1/3 was right, however where did the k lamda come from?

Thanks.

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#6

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Yes, so I think thats what the question is asking me to do (my first time doing M1 and vectors...)

Your answer of -1/3 was right, however where did the k lamda come from?

Thanks.

**DOJO**)Yes, so I think thats what the question is asking me to do (my first time doing M1 and vectors...)

Your answer of -1/3 was right, however where did the k lamda come from?

Thanks.

Because if a vector is parallel to another vector, it can be expressed by that vector multiply a real number.

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(Original post by

You confused of the first line a+l.b = ki?

Because if a vector is parallel to another vector, it can be expressed by that vector multiply a real number.

**BCHL85**)You confused of the first line a+l.b = ki?

Because if a vector is parallel to another vector, it can be expressed by that vector multiply a real number.

Here was my working before I posted on :

a + lb = (2i + j) + l(i+3j)

and then I did I multiplied out of b with l :

a + lb = (2i + j) + l(i+3j) =

(2i+j) + (li + 3lj)

and then my friend it all went horribly wrong... However by looking at your working I was not far away from getting the right answer...

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#8

(Original post by

I understand the a+l.b , its just the kl , where did k come from?

Here was my working before I posted on :

a + lb = (2i + j) + l(i+3j)

and then I did I multiplied out of b with l :

a + lb = (2i + j) + l(i+3j) =

(2i+j) + (li + 3lj)

and then my friend it all went horribly wrong... However by looking at your working I was not far away from getting the right answer...

**DOJO**)I understand the a+l.b , its just the kl , where did k come from?

Here was my working before I posted on :

a + lb = (2i + j) + l(i+3j)

and then I did I multiplied out of b with l :

a + lb = (2i + j) + l(i+3j) =

(2i+j) + (li + 3lj)

and then my friend it all went horribly wrong... However by looking at your working I was not far away from getting the right answer...

You just need to group i and j into 2 groups .. then find l.

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(Original post by

Right, k is just put there. k can be any real value. (You can find it after solving l = -1/3, k = 2 + l)

You just need to group i and j into 2 groups .. then find l.

**BCHL85**)Right, k is just put there. k can be any real value. (You can find it after solving l = -1/3, k = 2 + l)

You just need to group i and j into 2 groups .. then find l.

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(Original post by

Oh right , I now see what you have done, you basically did what I did, but then made lamba in b the subject of the equation to get -1/3

**DOJO**)Oh right , I now see what you have done, you basically did what I did, but then made lamba in b the subject of the equation to get -1/3

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#11

(Original post by

Just a quick question, do i have to draw questions like this, or can I just get away with algebra? Because when I started this question, I thought by drawing the vectors would make things better, but it made it more confusing....

**DOJO**)Just a quick question, do i have to draw questions like this, or can I just get away with algebra? Because when I started this question, I thought by drawing the vectors would make things better, but it made it more confusing....

a + l.b = ki where k E R.

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(Original post by

Erhh, I think you just can write because a+l.b is parallel to vector i, so

a + l.b = ki where k E R.

**BCHL85**)Erhh, I think you just can write because a+l.b is parallel to vector i, so

a + l.b = ki where k E R.

Thanks!

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