Year 13 Maths Help Thread

Draw a big diagram showing the origin and draw all of the position vectors. To find the coordinates of D you need the position vector of D i.e. you need the vector OD.

Think about GCSE vector pathways to find a vector path which takes you from O to D. If you've drawn a good diagram with all the information on it then this shouldn't be too hard.

If you're stuck, please post the diagram that you have drawn.

Yes RDK I know I know I'm Sorry,

Im just all over the place today

Vdu + Udv

why cant you draw a parallelogram with A, B, C, D instead? I dont understand why it has to be from O??

why cant you draw a parallelogram with A, B, C, D instead? I dont understand why it has to be from O??

He's not saying it has to be from O... he said to draw a diagram including the origin. Not that the parallelogram has to start from the origin.

However the coordinate D is given by the position vector OD by definition, which is why it's good to have the origin drawn on in the diagram, so you can figure out where D is and hence what OD is.

You need A, B, C and D on your diagram. But you should also include an origin somewhere (choose some random place on your diagram). Then finding the coordinates of D is equivalent to finding the vector OD.

Sorry for the bad diagram. Like this?

Preferably with axes :P

Sorry for the bad diagram. Like this?

Preferably with axes :P

Not sure if axes are useful here, especially since the coordinates are 3d?

Oh yeah, oops :3

Ok so now i have the diagram. How do i know what direction the vectors and what do i do next?

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ABCD is the parallelogram which means that A should be connected to B and B should be connected to C etc.

Draw the vector OD on your diagram because this is what you're trying to find. Also draw on OA, OB and OC because you are given these in the question (they're coordinates but that's basically the same as a position vector). Also notice that you've already found the vector BA.

See if you can use GCSE vectors to come up with a vector path to find OD.

Sorry i completely missed your reply. Like this?

BA = (-2, -6, 4)

OD = OA + AB + BC + CD ??

i feel like im doing something wrong here

Good diagram.

From here you could notice that vector CD is equal to BA since it is a parallelogram.

But it's quicker to use this path:

OD = OC + CD.

Since you've already worked out vector BA in an earlier part, this method is the quickest.

Ah i see. So:

OD = (11,6, -4) + (-2, -6, -4)

= (9, 0, 0) so coordinates of D are (9, 0, 0)

NOTE: I would normally write this is vector form (but not the final answer). How do i know when to use vectors or when to use coordinates (on certain questions the mark scheme alternates between both).

Can someone help me with parametric equation question. I'm not sure where to go from here. thank you so much!

Start with the first one : you can rewrite them like this:

$\displaystyle x=(e^t)^2$

$\displaystyle y=\frac{3}{e^t}$

Does that help?

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