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# Edexcel Core 3 - 21st June 2016 AM watch

1. (Original post by khaleesi98)
Ok so first think about it in terms of what k could be if there were solutions...
g(θ) = Rcos(2θ-α) = k
-1 < cos(2θ-α) < 1
so
-R < Rcos(2θ-α) < R
ie. -R < k < R

But as there aren't solutions...
k < -R, k > R
What if it said when k has only one solution? And likewise, if k has only two solutions?
2. Not sure if it's been asked already, but what do you do on a cast diagram if tan theta = a negative value?
E.G. Tan(theta)=(-1/3)pi

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3. (Original post by nnblccz)
Not sure if it's been asked already, but what do you do on a cast diagram if tan theta = a negative value?
E.G. Tan(theta)=(-1/3)pi

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I'm not sure about others but when I get a negative value, in my calculator I get the inverse of the positive version and then that is the negative angle (if that makes sense). So in the cast diagram the angle that is met by the horizontal line is the angle on the calculator. From there you can easily work out all of the negative values for that particular angle!

Good luck for tomorrow
4. Alright guys, this is it! Good night and good luck for tomorrow
5. (Original post by JustAnotherExam)
I'm not sure about others but when I get a negative value, in my calculator I get the inverse of the positive version and then that is the negative angle (if that makes sense). So in the cast diagram the angle that is met by the horizontal line is the angle on the calculator. From there you can easily work out all of the negative values for that particular angle!

Good luck for tomorrow
I kind of get it, but could you possibly explain it a bit more detail? Do you inverse the value that you get, and then put that on the cast diagram?

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Good luck to you too!
6. When transforming a graph do u always do the stretch first and then the translation (moving it sideways/up/down etc? Is this a 'rule'?
7. Help with part D
Attached Images

8. (Original post by Tow)
What if it said when k has only one solution? And likewise, if k has only two solutions?
Ok I knew the answer to the original q but I wouldn't trust me too much on anything else 😅 For what it's worth, though, I don't think those things would make sense in this question. If it's possible for g(θ) to = k, then surely there are going to be an infinite no. of solutions, as there was no range given for θ.
Attached Images

10. (Original post by khaleesi98)
Ok I knew the answer to the original q but I wouldn't trust me too much on anything else 😅 For what it's worth, though, I don't think those things would make sense in this question. If it's possible for g(θ) to = k, then surely there are going to be an infinite no. of solutions, as there was no range given for θ.
I saw a question in a past paper like this but I'm sure it asked if k only had one solution. I really don't know which one it is from though!!
11. (Original post by Marccs)
Help with part D
Hi part d isn't shown in the attachment
12. (Original post by Marccs)
Help with part D
Where did you get that from?

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13. (Original post by selenmer)
Hi part d isn't shown in the attachment
Sorry I meant part C
14. (Original post by khaleesi98)
Ok I knew the answer to the original q but I wouldn't trust me too much on anything else 😅 For what it's worth, though, I don't think those things would make sense in this question. If it's possible for g(θ) to = k, then surely there are going to be an infinite no. of solutions, as there was no range given for θ.
I've just found it, it's the June 2013R paper, Q3c.

Paper:
http://qualifications.pearson.com/co...e_20130613.pdf

MS:
http://qualifications.pearson.com/co...c_20130815.pdf
15. (Original post by Tow)
I saw a question in a past paper like this but I'm sure it asked if k only had one solution. I really don't know which one it is from though!!
Hmm I think you'd have to find the paper. Tbh though at this point we'd probably all be better just going to bed ☺️ good luck anyways x

** oh you did I'm having a look now
16. Thanks but does this not mean u have to show CAST OR GRAPH?

No need to show CAST.
Attached Images

17. (Original post by Marccs)
Help with part D
So after you differentiate T, you end up with -12e^-0.04t (I hope you've gotten to this stage). Then you should be thinking "I need to find a way to express it fully in terms of T and get rid of/replace t". Then you ought to realise that you can rearrange the original equation T=300e^-0.04t + 20 to make e^-0.04t the subject, and then once you've done that, sub that in to your differential equation
18. Sorry to anyone who tagged or replied to me, just been out watching Wales. I can help with any queries anyone may have, but there may be mistakes due to drunkenness (probably not though).
19. (Original post by WinterApproaches)
So after you differentiate T, you end up with -12e^-0.04t (I hope you've gotten to this stage). Then you should be thinking "I need to find a way to express it fully in terms of T and get rid of/replace t". Then you ought to realise that you can rearrange the original equation T=300e^-0.04t + 20 to make e^-0.04t the subject, and then once you've done that, sub that in to your differential equation
Thanks
20. (Original post by 13 1 20 8 42)
Sorry to anyone who tagged or replied to me, just been out watching Wales. I can help with any queries anyone may have, but there may be mistakes due to drunkenness (probably not though).
Jw. Someone posted this:
http://www.thestudentroom.co.uk/atta...6&d=1466461962

for d) would you look at when cos does 2 repeats and then find t for that, assuming you let theta = pi(t)/5?

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