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# Maths C3 - Trigonometry... Help?? Watch

1. for part (e) where do I go from?...

2. (Original post by Philip-flop)

for part (e) where do I go from?...

Have you tried anything from here? Do some manipulation of the equation and see what happens.

Post our working if you get stuck.
3. (Original post by notnek)
Have you tried anything from here? Do some manipulation of the equation and see what happens.

Post our working if you get stuck.
I still couldn't manage to work it out so I moved on to the other questions
4. (Original post by Philip-flop)
I still couldn't manage to work it out so I moved on to the other questions
Multiply both sides by

Then you reaarange and eventually you have something in the form

Where a, b and c are constants,

Now you factorise or use quadratic fotmula
5. (Original post by asinghj)
Multiply both sides by

Then you reaarange and eventually you have something in the form

Where a, b and c are constants,

Now you factorise or use quadratic fotmula
OMG thank you so much!! Managed to work it out now
6. Where have I gone wrong for part (b)?...

Attachment 585308585310
Attached Images

7. (Original post by Philip-flop)
Where have I gone wrong for part (b)?...

Attachment 585308585310
Recheck how you got from 3rd line to 4th line
8. (Original post by asinghj)
Recheck how you got from 3rd line to 4th line
Thank you so much!! I was stressing about this question so much to the point where I couldn't even think straight! I got there in the end
9. Can someone help me? I'm stuck on part (h) and (i)...

For part (h) I've done....

For part (i) I've done...

<<<or should I re-arrange this line to give...???

<<< I know the double angle formula... ... but this can't be used here, right?

Don't know where to go from there for either of them though

Edit: I've managed to work out part (i) now by rearranging the second line from my workings above
10. (Original post by Philip-flop)
Can someone help me? I'm stuck on part (h) and (i)...
For h, multiply top and bottom by and use identities for double angles. Also it will be useful to rewrite as
11. (Original post by Philip-flop)
Can someone help me? I'm stuck on part (h) and (i)...

For part (h) I've done....

For part (i) I've done...

<<<or should I re-arrange this line to give...???

<<< I know the double angle formula... ... but this can't be used here, right?

Don't know where to go from there for either of them though

Edit: I've managed to work out part (i) now by rearranging the second line from my workings above
For h), the quickest way is to use the tan/sec identity on the denominator and then compare what you've got with

12. (Original post by RDKGames)
For h, multiply top and bottom by and use identities for double angles. Also it will be useful to rewrite as
Ok so this is what I've done for part (h) now...

But then where from here?

(Original post by notnek)
For h), the quickest way is to use the tan/sec identity on the denominator and then compare what you've got with

Ok, following your way for part (h) I've done...

But then I'm having trouble comparing it to the double angle formula...

I can only vaguely see why it becomes...

Is it because from the identity you would have to times by -1 and divide by 2 to get the identity into the same form as ???
13. (Original post by Philip-flop)
Ok so this is what I've done for part (h) now...

But then where from here?

Ok, following your way for part (h) I've done...

But then I'm having trouble comparing it to the double angle formula...

Multiply this by 2:

Then multiply it by -1, which is the same as multiplying the denominator by -1:

Does that help?

A lot of this exercise is about comparing expressions with the double angle identities. This question is one of the trickier ones.
14. (Original post by Philip-flop)
Is it because from the identity you would have to times by -1 and divide by 2 to get the identity into the same form as ???
That's correct - you got it before my reply
15. (Original post by notnek)

Multiply this by 2:

Then multiply it by -1, which is the same as multiplying the denominator by -1:

Does that help?

A lot of this exercise is about comparing expressions with the double angle identities. This question is one of the trickier ones.
Thank you so much! I had a feeling I might have to compare it to that double-angle formula, but it took me a while to realise it at first!
16. (Original post by Philip-flop)
Ok so this is what I've done for part (h) now...

But then where from here?
If you turn tan into sine over cosine then you are left with sin(x)cos(x). As I mentioned above, manipulating this slightly will enable you to use double angle formulae.
17. (Original post by RDKGames)
If you turn tan into sine over cosine then you are left with sin(x)cos(x). As I mentioned above, manipulating this slightly will enable you to use double angle formulae.
Omg yes!! Thank you!! I've managed to get there now I seized up at first, but then re-arranged tan like you said and it was pretty simple from there. Really appreciate the help
18. Ok, so I spent way too much time trying to solve this question last night without any luck....

I've tried comparing to the double angle formula for

I can see that needs to be divided by 4 in order to get

so this means...

Divide by 4 gives...

.... right??

And then I have to sub into the equation I've just found above??
19. (Original post by Philip-flop)
Ok, so I spent way too much time trying to solve this question last night without any luck....

I've tried comparing to the double angle formula for

I can see that needs to be divided by 4 in order to get

so this means...

Divide by 4 gives...

.... right??

And then I have to sub into the equation I've just found above??
You are not dividing tan by 4, you are dividing the angle. So
20. (Original post by RDKGames)
You are not dividing tan by 4, you are dividing the angle. So
Thanks for making realise that! I'm still a little stuck on this question though

If how do I find ?

Sorry if I'm sounding pretty silly, but I've never come across a question like this

Updated: April 23, 2017
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