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- May 4th 2009, 03:26 AMAquafinaObtuse angle is Right Angle
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- May 5th 2009, 01:01 AMGrandad
Hello AquafinaThis is an interesting one. It shows that you can't rely on a diagram to tell the whole truth.

In fact, if you draw the diagram carefully, you'll find that the line $\displaystyle PD$ lies outside the quadrilateral - see the attached.

You'll then find that instead of $\displaystyle x = \angle PBC - \angle PBA$, you get $\displaystyle x = 360-(\angle PBC + \angle PBA)$, which is quite a different matter!

Grandad - May 5th 2009, 03:11 AMAquafina
hi thanks thats exactly what i got, but wasnt sure if it was just the case in the way I was drawing it, and maybe if the line can come inside for certain lengths

also, since it says that there is a mistake in the proof, can we assume that the mistake is not in the proof, but actually in the diagram, as an answer? - May 5th 2009, 09:44 AMGrandad
- May 5th 2009, 10:08 AMAquafina
thanks!

do u have any ideas on this question that i posted earlier:

http://www.mathhelpforum.com/math-he...-integers.html

I was clueless on the 2nd bit.. - May 9th 2009, 04:41 AMAquafina
hi

i need to say why the proof doesnt work because of the reason shown, i.e. it is drawn convectly?

what can i say about this?