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Maths C3 - Trigonometry... Help?? Watch

1. Ok. How do I even do part (c) and (d)??

For part (c)... Shall I start off by using the fact that...
?
2. ^ Anyone??
3. (Original post by Philip-flop)
Ok. How do I even do part (c) and (d)??

For part (c)... Shall I start off by using the fact that...
?
Look back at question 5H that you did successfully a few days back.

You need to use again to write the fraction in the form

For d), use the fact that

These are all quite tricky questions that you don't really see in exams. Don't worry too much if you find them hard.
4. (Original post by notnek)
Look back at question 5H that you did successfully a few days back.

You need to use again to write the fraction in the form

For d), use the fact that

These are all quite tricky questions that you don't really see in exams. Don't worry too much if you find them hard.
Yeah I had a feeling that part (c) was similar to Question 5(h) that I did not long ago. Managed to figure that one out now. But am still stuck on part(d).

Thanks a lot for your help
5. (Original post by Philip-flop)
Yeah I had a feeling that part (c) was similar to Question 5(h) that I did not long ago. Managed to figure that one out now. But am still stuck on part(d).

Thanks a lot for your help

Try substituting these to get something of the form
6. (Original post by notnek)

Try substituting these to get something of the form
Oh yeah of course! I actually started doing that then realised. So I've done...

Alternatively I could have done....

Am I right??
7. (Original post by Philip-flop)
Oh yeah of course! I actually started doing that then realised. So I've done...

Alternatively I could have done....

Am I right??
Yes that's all correct.

And another way you can see that those two forms are equivalent is by using

:

8. (Original post by notnek)
Yes that's all correct.

And another way you can see that those two forms are equivalent is by using

:

Oh yeah! Because sin is a translation of cos by 90 degrees (to the right) parallel to the x-axis, correct?

Thanks again! Things are definitely making sense now
9. (Original post by Philip-flop)
Oh yeah! Because sin is a translation of cos by 90 degrees (to the right) parallel to the x-axis, correct?

Thanks again! Things are definitely making sense now
That's basically correct although a shift of by to the right gives

But as you discovered in an older post, cos is an even function so you have

10. (Original post by notnek)
That's basically correct although a shift of by to the right gives

But as you discovered in an older post, cos is an even function so you have

Yes, cos is an "even function" due to it's symmetry on either side of the y-axis. Whereas sin is an odd function.
11. Ok so I'm stuck again already

Have I even been doing this one right??
Attachment 584984584986

Then I don't really know where to go from there.
Attached Images

12. (Original post by Philip-flop)
Ok so I'm stuck again already

Have I even been doing this one right??
Attachment 584984584986

Then I don't really know where to go from there.
You have on one side of the equation and on the other.

You can move them to the same side and combine them.
13. (Original post by notnek)
You have on one side of the equation and on the other.

You can move them to the same side and combine them.
Yeah I thought about doing that, so...

But then I had no idea where to go from there so I just assumed I was wrong
14. (Original post by Philip-flop)
Yeah I thought about doing that, so...

But then I had no idea where to go from there so I just assumed I was wrong
Now divide by cosine to get tan and solve it that way.
15. (Original post by RDKGames)
Now divide by cosine to get tan and solve it that way.
Omg, I'm actually going to kick myself!! Managed to get there in the end.

and then solved it from there to get...

Thank you RDKGames and notnek I'm forever grateful for your help!!

16. For part (c) should I start by doing?...

and then should I times by cos(45)?? Or am I being completely retarded here? actually have no idea what I'm doing.
Why do I suck at trigonometry?
17. (Original post by Philip-flop)

For part (c) should I start by doing?...

and then should I times by cos(45)?? Or am I being completely retarded here? actually have no idea what I'm doing.
Why do I suck at trigonometry?
Since we have

and

Try using this here and look out for angle sum of 90 in future questions - you need it in different types of trig questions.

Also, don't immediately change into unless you think it will be useful. It was useful for a couple of questions that you've done but not here.
18. (Original post by notnek)
Since we have

and

Try using this here and look out for angle sum of 90 in future questions - you need it in different types of trig questions.

Also, don't immediately change into unless you think it will be useful. It was useful for a couple of questions that you've done but not here.
Ohhhh I see.

I never knew that if... where a and b sum up to 90 degrees that...
Again, the book fails to explain any of that!

Ok, so for this question I would do?...

But then where from there? :/
19. (Original post by Philip-flop)
Ohhhh I see.

I never knew that if... where a and b sum up to 90 degrees that...
Again, the book fails to explain any of that!

Ok, so for this question I would do?...

But then where from there? :/
From there is just a number you can work out on your calculator. So you can move it to the other side along with the .

The 'adding to 90' rule is just an application of the identity e.g. where x is 25.
20. (Original post by notnek)
From there is just a number you can work out on your calculator. So you can move it to the other side along with the .

The 'adding to 90' rule is just an application of the identity e.g. where x is 25.
Thank you! Not sure why I panicked when I saw...

Updated: April 23, 2017
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