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Trig - I'm stuck

This is not a TeeEm thread - I'm genuinely stuck :smile:

The question : AB = AC. Find the value of theta. Ignore the 'b' in the diagram - not relevant to the question.



A teacher gave this question to one of my tutees, probably not realising how hard it is. The best I've done is get to a quartic but I could've made a mistake and I couldn't solve the quartic directly anyway.

Help!

(Please post any solutions in spoilers)
(edited 8 years ago)

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no thanks :afraid:
that is not a fun looking question...

just had a very brief attempt but got scared off pretty quickly xD
What study level is this?
Original post by notnek
This is not a TeeEm thread - I'm genuinely stuck :smile:

The question : AB = AC. Find the value of theta.



A teacher gave this question to one of my tutees, probably not realising how hard it is. The best I've done is get to a quartic but I could've made a mistake and I couldn't solve the quartic directly anyway.

Help!


doesn't seem too difficult i'm doing it currently
Reply 4
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Notnek
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Original post by thefatone
doesn't seem too difficult i'm doing it currently

I could just be being stupid.
Original post by notnek
I could just be being stupid.


oops i made a mistake xD
Reply 6
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Notnek
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Original post by surina16
What study level is this?

The student who was given this question is in Year 13 doing A Level Maths (not further maths).

I have no idea where the teacher got the question from or if they made it themselves.
Original post by notnek
This is not a TeeEm thread - I'm genuinely stuck :smile:

The question : AB = AC. Find the value of theta.



A teacher gave this question to one of my tutees, probably not realising how hard it is. The best I've done is get to a quartic but I could've made a mistake and I couldn't solve the quartic directly anyway.

Help!

(Please post any solutions in spoilers)


Are we solving it in terms of b or is b to be determined somehow?
Reply 8
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Notnek
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Original post by morgan8002
Are we solving it in terms of b or is b to be determined somehow?

Finding it in terms of b would be too easy!

No you're meant to find the theta angle. The 'b' is not relevant to the question.
Original post by notnek
Finding it in terms of b would be too easy!

No you're meant to find the theta angle. The 'b' is not relevant to the question.


i'm certain i haven't done this right, i don't think i can actually do this............
presumably you mean find theta in terms of b

:holmes:
Original post by notnek
Finding it in terms of b would be too easy!

No you're meant to find the theta angle. The 'b' is not relevant to the question.


I got

Spoiler

I have no idea if that's right though. I'm attempting to check but it's a mess.

edit: No it was wrong. I have another idea though.
(edited 8 years ago)
Reply 12
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Notnek
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Original post by the bear
presumably you mean find theta in terms of b

:holmes:

You wish.
Original post by notnek
The student who was given this question is in Year 13 doing A Level Maths (not further maths).

I have no idea where the teacher got the question from or if they made it themselves.


Explains why I could only get this far with my limited gcse knowledge :biggrin: (which is still wrong)



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1457277956625.jpg29.9KB
Original post by morgan8002
I got

Spoiler

I have no idea if that's right though. I'm attempting to check but it's a mess.


just checking how that would fit with the other angles around the triangle suggest that you're right,granted i could've made a mistake checking to see if you made one
Original post by drandy76
just checking how that would fit with the other angles around the triangle suggest that you're right,granted i could've made a mistake checking to see if you made one


It would fit. 90 is correct
Original post by drandy76
just checking how that would fit with the other angles around the triangle suggest that you're right,granted i could've made a mistake checking to see if you made one


There's a chance it's correct, but there was a mistake in my working.
Original post by morgan8002
I got

Spoiler

I have no idea if that's right though. I'm attempting to check but it's a mess.

edit: No it was wrong. I have another idea though.


Wha?

I just checked using the sine and cosine rules and 90 was fine :redface:
Original post by morgan8002
I got

Spoiler

I have no idea if that's right though. I'm attempting to check but it's a mess.

edit: No it was wrong. I have another idea though.


M8 me and @student403 already vouched pls dont dis this
Original post by Student403
Wha?

I just checked using the sine and cosine rules and 90 was fine :redface:


I'm pretty confused. My last line of working was cos⁡θ2=0\cos \frac{\theta}{2} = 0, which I wrote down the wrong solution θ=90o\theta = 90^o. There was something else that could have been 0 instead which I'm working on now, but I don't see any reason why I would accidentally come up with the right answer.

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