# Vector..

• May 14th 2013, 05:51 AM
Trefoil2727
Vector..
Given that a=3i-2j, b=3i+j and c=-6i+j, express pa-qb in terms of p,q,i and j. Hence, find the value of p and of q if pa-qb is equal to the unit vector along the straight line 4x+3y=12
• May 14th 2013, 06:08 AM
Plato
Re: Vector..
Quote:

Originally Posted by Trefoil2727
Given that a=3i-2j, b=3i+j and c=-6i+j, express pa-qb in terms of p,q,i and j. Hence, find the value of p and of q if pa-qb is equal to the unit vector along the straight line 4x+3y=12

Do you intend to show any of your own work?
• May 16th 2013, 11:13 PM
Trefoil2727
Re: Vector..
well, I have to admit that I don't know how to solve it..
• May 16th 2013, 11:22 PM
MINOANMAN
Re: Vector..
Trefoil it is simple...
what pa means?
what qb means?

multiplicationnnnn..........so as Plato suggests........ just do itttttttttttttttttttttt .

• May 17th 2013, 08:10 AM
HallsofIvy
Re: Vector..
You are told exactly what to do: you are given pa+ qb and you are told that a= 3i-2j, b=3i+j. It's just integer arithmetic.
• May 30th 2013, 11:08 PM
millakinross
Re: Vector..
this interesting

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• Jun 8th 2013, 03:07 AM
jacobpitt
Re: Vector..
Really good one question and i don't solve this question and if you know the answer just share with me.
• Jun 8th 2013, 05:13 AM
HallsofIvy
Re: Vector..
Quote:

Given that a=3i-2j, b=3i+j and c=-6i+j, express pa-qb in terms of p,q,i and j. Hence, find the value of p and of q if pa-qb is equal to the unit vector along the straight line 4x+3y=12
Since it has been a while: It is, as I said, integer arithmetic. pa= p(3i- 2j)= 3pi- 2pj. qb= q(3i+ j)= 3qi+ qj. pa- qb= 3pi- 2pj- (3qi+ qj)= (3p- 3q)i-(2p+ q)j.

A vector pointing along the straight line 4x+ 3y= 12 is 4i+ 3j which has length $\sqrt{4^2+ 3^2}= 5$ so a unit vector in that direction is (4/5)i+ (3/5)j

We have (3p- 3q)i- (2p+ q)j= (4/5)i+ (3/5)j so solve 3p- 3q= 4/5 and -2p- q= 3/5 for p and q.