You are Here: Home >< Maths

# Anyone need help with any *EDEXCEL* C3 and C4 past paper questions? watch

Mixed Exercise 7F. Q6. part e. + part f.

I looked at the first line of the answers in hope that it'd click in my mind and i could do the rest of the proof. But i still can't

Thank you
+ rep.
2. ^ Can you post the question?
3. (Original post by Apple24)
^ Can you post the question?
Sure

Show that :

1-cos2x
--------- = (sec^2 x -1 )
1+cos2x

EDIT: I posted the wrong one! sorry!!

this is the one i'm stuck on:

show that:

sin(x+y)sin(x-y) = coz^2y - cos^2x
4. Use cos2x=(1-2sin^2x) on the top, and cos2x=(2cos^2x-1) on the bottom.
These will cancel out the 1's and it'll look a bit nicer then!
5. (Original post by Apple24)
^ Can you post the question?
Sorry, posted the wrong question.
I've edited the post, with the right one now.
6. (Original post by matty92)
Use cos2x=(1-2sin^2x) on the top, and cos2x=(2cos^2x-1) on the bottom.
These will cancel out the 1's and it'll look a bit nicer then!
Thanks. Had a slightly blonde moment and posted the question i just did
7. I think this question would be to do with the trig identity that cosA-cosB=-2sin(a+b/2)sin((a-b)/2)?

I will re-edit later if I get it!
8. (Original post by time.to.dance)
Thanks. Had a slightly blonde moment and posted the question i just did
Haha. Where have you got upto on this one? I started with multiplying out using the addition formula sin(a+b)=sina.cosb+cosa.sin.b It does actually cancel down a bit.
9. (Original post by matty92)
Haha. Where have you got upto on this one? I started with multiplying out using the addition formula sin(a+b)=sina.cosb+cosa.sin.b It does actually cancel down a bit.
Nowhere! i've been staring at it for 10 mins now couldn't figure out the first step.
Thanks for that! i'll attempt it again now
10. Expand

=

=

...
11. (Original post by matty92)
Expand

=

=

...
Thank you! i've done it now i'll rep as soon as i can
12. (Original post by matty92)
Haha. Where have you got upto on this one? I started with multiplying out using the addition formula sin(a+b)=sina.cosb+cosa.sin.b It does actually cancel down a bit.
I'm stuck on the next question now oh god that maths prediction does not look so promising

tan[(pie/4)+x] - tan[(pie/4) -- x] = 2tan2x (not to the power)

sunday evening is not the time for last minute maths homework either

Any help would be really appreciated
13. how do I prove that: cot2x + cosec2x = cotx ????

14. ^Change cot and cosec into cos and sins and try and simplify.
15. (Original post by W.H.T)
how do I prove that: cot2x + cosec2x = cotx ????

1/tan2x + 1/sin2x

= cos2x/sin2x + 1/sin2x

= (1+cos2x)/sin2x

= (2cosx^2 - 1 + 1)/2sinxcosx

= 2cos^2x/2sinxcosx

cancle by 2cosx

= cosx/sinx

= cotx
16. just a quick question as i cant seem to interpret what the MS has done..

1b) Find the exact solutions to the equation:

e^x+3e^-x = 4

i do know that i had to turn it into an quadratic equations however how does the mark scheme manage to change the 4 and the 3 around so there isnt a e^-x?

(e^x)^2 - 4e^x + 3 = 0

thanks!
17. Because you're multiply both sides by e^x.

(e^x)(e^x) + 3(e^-x)(e^x) = 4(e^x)
18. (Original post by time.to.dance)
I'm stuck on the next question now oh god that maths prediction does not look so promising

tan[(pie/4)+x] - tan[(pie/4)+x] = 2tan2x (not to the power)

sunday evening is not the time for last minute maths homework either

Any help would be really appreciated
Nope maybe not the best time...
Probably a bit late now but, its a bit of a strange question... doesn't the cancel to make zero?

So we're proving that or am I just completely misinterpreting it?
19. (Original post by matty92)
Nope maybe not the best time...
Probably a bit late now but, its a bit of a strange question... doesn't the cancel to make zero?

So we're proving that or am I just completely misinterpreting it?
Ahh it was rather late yesterday I've edited it now. It was meant to be a minus before the x in the second bracket.
20. Good luck everyone

TSR Support Team

We have a brilliant team of more than 60 Support Team members looking after discussions on The Student Room, helping to make it a fun, safe and useful place to hang out.

This forum is supported by:
Updated: February 21, 2010
Today on TSR

### Results day under a month away

How are you feeling?

Poll
Useful resources

### Maths Forum posting guidelines

Not sure where to post? Read the updated guidelines here

### How to use LaTex

Writing equations the easy way

### Study habits of A* students

Top tips from students who have already aced their exams