Edexcel A2 C4 Mathematics June 2015 - Official Thread

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Reply 720

ACarter8

Can someone help me with question 7c. It's from solomon sheets on vectors.

Reply 721

randlemcmurphy

Original post by ACarter8

Can someone help me with question 7c. It's from solomon sheets on vectors.

I haven't actually done it, but this is what I would do, from the equation of line l₂ we can form a position vector for R in terms of t. As you have worked out the position vectors of P and Q, you can work out the distance. As we know that PQ=QR, work out the vector QtoR, this will of course be in terms of t. Then work out the distance, however this distance will be equal to PQ, then solve for 2, if will be a quadratic so you should get two values (hopefully this is right!)

EDIT: Just realized that a quicker method is just to use the direction vector of l₂ and see what multiple it is of the distance PQ, and then do +/- of that.

(edited 8 years ago)

Reply 722

ACarter8

Original post by randlemcmurphy

The ms was your edited answer, still don't get it really.

EDIT: lol it's just clicked. Thanks for the help :smile:

(edited 8 years ago)

Reply 723

ridirahman

Can someone help me with this question please????

Reply 724

InOrbit

Original post by ridirahman

Can someone help me with this question please????

Two approaches:
1. Use the double angle formula multiple times and expand out. Long and arduous?

Use these sneaky factor formula that a lot of schools omit from teaching.

Try the sin A - sin B one.

(edited 8 years ago)

Reply 725

TeeEm

Original post by Alex:

Two approaches:
1. Use the double angle formula multiple times and expand out. Long and arduous?

Use these sneaky factor formula that a lot of schools omit from teaching.

Try the sin A - sin B one.

There is a far cleverer way of doing this ...

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Reply 726

username1162972

Original post by TeeEm

There is a far cleverer way of doing this ...

I know it... Hehe.

Posted from TSR Mobile

Reply 727

TeeEm

Original post by physicsmaths

I know it... Hehe.

Posted from TSR Mobile

I should hope so, otherwise no Cambridge ...
You will end up going to UCL like me since Imperial also rejected you ...

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Reply 728

InOrbit

Original post by TeeEm

There is a far cleverer way of doing this ...

I don't see a quicker method of approaching this without using the factor formulae. Care to share?

EDIT: Is it something obvious like taking one sin to the other side and inverse sin both sides?

(edited 8 years ago)

Reply 729

TeeEm

Original post by Alex:

I don't see a quicker method of approaching this without using the factor formulae. Care to share?

EDIT: Is it something obvious like taking one sin to the other side and inverse sin both sides?

kind of if it is done properly ...

Reply 730

InOrbit

Original post by TeeEm

kind of if it is done properly ...

Rearrange
sin5x = -sinx

Since sin is an odd function:
sin5x = sin-x

+2kpi and (2k+1)pi need to be considered

To be honest, the factor formulae are probably easier, as you have to consider the periodic nature of the sin graph as well as the rotational symmetry of the sin graph.

Reply 731

TeeEm

Original post by Alex:

It depends on your level ...

Reply 732

InOrbit

Original post by TeeEm

It depends on your level ...

That's true. I've always found it very dirty to be using inverse trig functions when both sides have trig functions. I am probably one of the very few people who use the factor formulae.

Reply 733

Brubeckian

Original post by TeeEm

I should hope so, otherwise no Cambridge ...
You will end up going to UCL like me since Imperial also rejected you ...

Brutal AF

Reply 734

TeeEm

Original post by Brubeckian

Brutal AF

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Reply 735

TeeEm

Original post by Alex:

That's true. I've always found it very dirty to be using inverse trig functions when both sides have trig functions. I am probably one of the very few people who use the factor formulae.

I would agree that you must use a technique appropriate to the standard of the question and never show off...
There are only marks for correct answers (no marks for bravery unfortunately)