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Please help with me with this circle problem.

Hello TSR - first post!

I've got this problem from a revision book I can't seem to work out. I'm struggling to find a relevant theorem - it can't be the alternative segment theorem because they are different triangles.

I'm less concerned about the answer, but more about how to work it out. I know you're all busy, so any response would be much appreciated.

4tEfY.png
Reply 1
Original post by BTB10
Hello TSR - first post!

I've got this problem from a revision book I can't seem to work out. I'm struggling to find a relevant theorem - it can't be the alternative segment theorem because they are different triangles.

I'm less concerned about the answer, but more about how to work it out. I know you're all busy, so any response would be much appreciated.

4tEfY.png


Do you know about opposite angles in a cyclic quadrilateral?
Reply 2
Original post by Blazy
Do you know about opposite angles in a cyclic quadrilateral?


Yup, but to work out X, I'd need to know what the opposite angle was - at the moment, I only know that 70 degrees is part of that angle.

Maybe there's something I'm missing here.
Reply 3
Original post by BTB10
Yup, but to work out X, I'd need to know what the opposite angle was - at the moment, I only know that 70 degrees is part of that angle.

Maybe there's something I'm missing here.


Think about the triangle - you have a 90 degree angle, a 'x' angle, what must the third (missing) angle be?

EDIT: (See posts below about missing information)
(edited 10 years ago)
Reply 4
Original post by BTB10
Yup, but to work out X, I'd need to know what the opposite angle was - at the moment, I only know that 70 degrees is part of that angle.

Maybe there's something I'm missing here.


Opposite angles in a cyclic quadrilateral add up to 180. Hence:

70+x+20=18070+x+20=180

Hope that helps
Original post by BTB10
..


Is there any more information?

As it stands the right-angled triangle on the right is entirely defined, but the one on the left could be any right-angled triangle.

I'd suggest checking the wording of the question, and the diagram given to you for anything further.

Edit: Or am I being thick?

Edit2 It would seem not.
(edited 10 years ago)
Reply 6
Original post by ghostwalker
Is there any more information?

As it stands the right-angled triangle on the right is entirely defined, but the one on the left could be any right-angled triangle.

I'd suggest checking the wording of the question, and the diagram given to you for anything further.

Edit: Or am I being thick?


I think I agree with you here. This was the original diagram (without my own answers put on top) - thanks for your relies guys.

http://puu.sh/4tFDr.png
Reply 7
Original post by ghostwalker
Is there any more information?

As it stands the right-angled triangle on the right is entirely defined, but the one on the left could be any right-angled triangle.

I'd suggest checking the wording of the question, and the diagram given to you for anything further.

Edit: Or am I being thick?


I'd say that without further information, the angle is indeterminate, since we can move the 90 degree angle anywhere in the left semi-circumference, and hence arbitrarily choose the value of x20x-20 and hence the value of xx

Or am I being thick?
Reply 8
Original post by ghostwalker
Is there any more information?

As it stands the right-angled triangle on the right is entirely defined, but the one on the left could be any right-angled triangle.

I'd suggest checking the wording of the question, and the diagram given to you for anything further.

Edit: Or am I being thick?


Original post by atsruser
I'd say that without further information, the angle is indeterminate, since we can move the 90 degree angle anywhere in the left semi-circumference, and hence arbitrarily choose the value of x20x-20 and hence the value of xx

Or am I being thick?


Nope, it's a valid observation :tongue:
Reply 9
Original post by atsruser
I'd say that without further information, the angle is indeterminate, since we can move the 90 degree angle anywhere in the left semi-circumference, and hence arbitrarily choose the value of x20x-20 and hence the value of xx

Or am I being thick?


Thats exactly thinking too! And I thought my maths was getting rusty!

But using that opposite corners add up to 180, I get a solution...hmm, need to look at it a bit more carefully.

I see my mistake. I think that this is unsolvable. Not enough information
(edited 10 years ago)
Reply 10
Given the fact that you have more info than necessary about the triangle on the right, and not enough on the left, it makes me very suspicious that the 70 degrees should, in fact, refer to the other angle at the top. Possibly.

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