Maths vectors as edexcel practice book question help!

username79352

https://imgur.com/a/tkVwEu9

Could anyone help me with this question please?

I don’t know how to solve it at all

Reply 1

davros

Original post by saminasb3

https://imgur.com/a/tkVwEu9
Could anyone help me with this question please?
I don’t know how to solve it at all

Have you done similar questions before?

What thoughts do you have on how you might try to find the value of k?

Reply 2

username79352

I have done but I don’t know what to do because oc and mc are unknown and when I try to make equations for a and b using that it’s to many unknowns.

Reply 3

username79352

I haven’t done questions where they have this many unknowns just the basic scalar and then equate a terms and b to find unknowns.

Reply 4

davros

Original post by saminasb3

I have done but I don’t know what to do because oc and mc are unknown and when I try to make equations for a and b using that it’s to many unknowns.

You need to set up some simultaneous equations and then it drops out not too bad!

Hint: how could you get from M to C via O? How can you get from A to N via O?

(Do you have the answers btw - I've worked this out quickly but would like to check my arithmetic.)

Reply 5

username79352

K is 0.6 and oc is 3b

Reply 6

username79352

When getting to mc via o the bit that I get stuck on is nc. I don’t understand what that could be or how to set up equations to find it out.

Reply 7

davros

Original post by saminasb3

K is 0.6 and oc is 3b

Great - I got k = 3/5 (i,e. 0.6) and OC = 3ON :smile:

Obviously you don't know OC in terms of ON to start with, so just write OC = mON where m is some unknown scalar and then try to set up your equations.

Reply 8

username79352

So I got an= -2a +b and mc is -a +b + nc

Reply 9

username79352

It’s what to do afterwards that I got stuck on when trying the question.

Reply 10

username79352

https://imgur.com/a/XJJ7PnI I got the answer but I’m not sure if my method is correct?

Reply 11

davros

Original post by saminasb3

https://imgur.com/a/XJJ7PnI I got the answer but I’m not sure if my method is correct?

can't quite follow that as you've written MC = MB + BN which isn't true, but I think you've got the right idea.

Personally I started with AB = AM + MB = -a + (1/5)MC and AN = AO + ON = -2a + b then writing MC in terms of MO and MC, but there may be other ways of reaching the same route :smile:

Reply 12

username79352

I get stuck on part b because I think my method is wrong for part a. Could you help me please?

Reply 13

username79352

Original post by davros

can't quite follow that as you've written MC = MB + BN which isn't true, but I think you've got the right idea.
Personally I started with AB = AM + MB = -a + (1/5)MC and AN = AO + ON = -2a + b then writing MC in terms of MO and MC, but there may be other ways of reaching the same route :smile:

I missed nc off

Reply 14

davros

Original post by saminasb3

I get stuck on part b because I think my method is wrong for part a. Could you help me please?

If you start with my last post using MC = MO + OC where OC = mON = mb, you can then write AB in 2 forms which gives you 2 equivalent forms and some simultaneous euations for a and b. One gives you k = 3/5 as per the answer, and then the value of m (which is the answer to the next question part) drops out immediately.

Have a go again and see how you get on :smile:

Reply 15

username79352

https://imgur.com/a/sRvZvYH is this the correct method?