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1. I really don't understand why bc has to be simplified. I got (9i+12j)+s(-3i-9j) and I don't get why the direction vector has to be simplified down to just I+3j in order to work out the constants. I used -3i-9j, it doesn't work. How am I supposed to know I have to simplify it to that extent ?? Thanks
2. (Original post by coconut64)
I really don't understand why bc has to be simplified. I got (9i+12j)+s(-3i-9j) and I don't get why the direction vector has to be simplified down to just I+3j in order to work out the constants. I used -3i-9j, it doesn't work. How am I supposed to know I have to simplify it to that extent ?? Thanks
is parallel to so you can use that as your direction vector in the equation of the line (since it has the same direction). But you could really use any vector parallel to this e.g. would work.

So you don't have to "simplify" the vector. Can you post your working when you used ? Because that should have worked.

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