GCSE Maths Question

[Gavin Chipper]

http://news.bbc.co.uk/1/hi/magazine/8081043.stm

Question 4 - what? Am I just being thick? It's the answer I gave but I don't get the explanation, nor can I see how that angle is set at any amount given the information.

[Michael Wallace]

Well it's using this rule, but their explanation seems a bit weird, since the way I'd do it is:

Y = 360 - X
Z = 180 - A (by this)
Y = 2Z

=> X = 360 - 2Z = 360 - 360 + 2A = 2A

But they seem to be answering the question "suppose X = 2A, show that opposite angles in a circle in a quadrilateral add up to 180".

[Gavin Chipper]

OK, so this hinges on that point being the centre of the circle which isn't mentioned in the question.

Edit - and yes, the explanation they give is shocking. "angles on a chord again" - again? That's the first time you've mentioned that phrase!

[Michael Wallace]

OK, so this hinges on that point being the centre of the circle which isn't mentioned in the question.

Yeah, that too.

[Charlie Reams]

Some of the questions seem to have been paraphrased, since I can't believe they'd write that way in a real exam. For example "What is this sum [9.02 x 10^-3] in standard form?" Well, it's already in standard form...

[Kai Laddiman]

Well it's using this rule

Er, that rule actually directly answers the question, stuff Y and Z

[Michael Wallace]

Well it's using this rule

Er, that rule actually directly answers the question, stuff Y and Z

Yeah true. My convoluted method was given rise to by their apparently incorrect one (for what it's worth, I couldn't remember precisely what this was off the top of my head, which possibly goes to show how important GCSE geometry becomes in later life, even if you do do a maths degree).