C4 vectors question

But how do you find the vectors BA and BC if you don't know what a and b are so you can't do e.g. BA = a - b etc..

But you do know they are given in the question

BA = BO + OA

or, as you have written it

BA = OA - OB


You said that you had done part (a) so surely you already know how to find the vectors AB and BC

Ah yes, I've got the answer now thank you! Sorry about being a pain, but I managed to get it in the end thanks to you!

If you're given the position vectors of 2 points X and Y then you can immediately write down the vector XY immediately by subtracting the position vector of X from that of Y.

There's no need to worry about drawing anything unless you find that sort of thing helpful - and in this case you seem to be more confused about the drawing process than actually following a method!

Simply work out BA and BC from the vectors given and then calculate the dot product

Oh okay, thank you!!

Do you mind telling me where I went wrong in this question?

I haven't checked your working (and it hurts my eyes to read sideways!) but have you used all the information given? There is a third equation that s and t must satisfy if the lines are to intersect - does this hold?

How do you know that you "went wrong" - do you have the answer for this question?

Yeah I understand that z must be equal in order for them to intersect and I know that I must have gone wrong somewhere because the answer says that they do intersect and the answer for s is different to mine..