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# Fp3 june 2010 - vectors watch

1. HI ALL.
Can anyone please explain how to do part c of question 7 on vectors. I am a little lost on how they got to the answer in the mark scheme.
Hope revision is going well.

Thanks
2. (Original post by DORI)
HI ALL.
Can anyone please explain how to do part c of question 7 on vectors. I am a little lost on how they got to the answer in the mark scheme.
Hope revision is going well.

Thanks
Which paper? Or post a link.
3. (Original post by B_9710)
Which paper? Or post a link.
https://3a14597dd5c7aa2363f067571766...%20Edexcel.pdf page 11

thanks
4. For FP3 there is a standard formula that gives you the shortest distance from a point to a line. Alternatively you could find an equation of the line from N that is perpendicular to PR. Then using the fact that the line you found the equation when dot multiplied with the direction of PR will be 0 you can find the value of the parameter which enables you to easily find the distance.
5. (Original post by B_9710)
Alternatively you could find an equation of the line from N that is perpendicular to PR. Then using the fact that the line you found the equation when dot multiplied with the direction of PR will be 0 you can find the value of the parameter which enables you to easily find the distance.
that's were I seem to be a little lost. I am trying to find the equation of the line from N to PR, but with no success!
6. (Original post by DORI)
that's were I seem to be a little lost. I am trying to find the equation of the line from N to PR, but with no success!
Well . So the parametric equation of the line PR, is . (I'm using i, j k notation as it is easier to do on here).
So if we let point B (arbitrarily chosen) lie on PR, such that NC is perpendicular to PR, then we realise that the point C is the point on PR that is closest to N. If N lies on PR then it must have coordinates that satisfies the equation of PR. Using properties of the scalar product you should be able to find the value of and then find the distance.
Please just say if you want me to clarify any of this.
7. (Original post by B_9710)
Well . (I'm using i, j k notation as it is easier to do on here).
should that not be lambda ( -5i -13j -3k).
Btw thanks so much for your help.
8. (Original post by DORI)
should that not be lambda ( -5i -13j -3k).
Btw thanks so much for your help.
Because is just a constant, it could be positive or negative, so it doesn't matter what the direction vector is as long as it is scaled correctly. It could be (-10i -26j 6k ) if you wanted it to be, you would just get different values so it would't matter at all.
9. (Original post by B_9710)
Because is just a constant, it could be positive or negative, so it doesn't matter what the direction vector is as long as it is scaled correctly. It could be (-10i -26j 6k ) if you wanted it to be, you would just get different values so it would't matter at all.
ok I see.

I've finally got it.

Thanks

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