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# Edexcel C4 June 2012 Vectors Q8 C) Watch

1. Hi, I'm stuck on this vectors question:

8c) The point c has position vector (3i+12j+3k)

The point P lies on l. Given that vector CP is perpendicular to l,
find the position vector of point P.

And other information I've got before this is
A (10i+2j+3k)
B (8i+3j+4k)
vector eqn of line l = (10,2,3)+λ(-2,1,1)

i tried exam solutions but i didn't understand what he was trying to explain, it seemed too long winded
2. From the looks of it you'd have to sub in P as (10-2s)i, (2+s)j, (3+s)k, and use the fact that you know cp is perp to l so the dot matrix of PC and the (-2s,s,s) =0, from there you just rearrange to find s and sub it into the equation of P. Idk if that's correct or if it helps but I think that's how it's done. GL
edit: it's *(-2,1,1) -- not (-2s,s,s)
3. (Original post by sdfvhgsrbf)
From the looks of it you'd have to sub in P as (10-2s)i, (2+s)j, (3+s)k, and use the fact that you know cp is perp to l so the dot matrix of PC and the (-2s,s,s) =0, from there you just rearrange to find s and sub it into the equation of P. Idk if that's correct or if it helps but I think that's how it's done. GL
edit: it's *(-2,1,1) -- not (-2s,s,s)

Thankyouuu, you're a star i'll give it a whirl

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