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# i cant prove this - should be simple watch

1. I have tried to do this but i just cant see how.
show that if Angle BPA has measue "a" then angle CPD has measure "a"
I have written equations such as "a" (which is angle APD) + BPC = 180 etc, is this the right track?

Edit : i know the picture is small - but if you click on it, you can see it more clearly
2. That depends what you're allowed to assume here. Most schools would allow you to write down without proof (because it's fairly 'obvious') that angle BPA = angle CPD - if you're not allowed to write that, you might not be allowed to write that angle BPA + angle APD = 180 degrees. Nonetheless, if you know that you are allowed to write that, it's the right way forward.

Otherwise: can you tell us what exactly you've been taught already, so that we can see how to help you?
3. (Original post by Hrov)
I have tried to do this but i just cant see how.
show that if Angle BPA has measue "a" then angle CPD has measure "a"
I have written equations such as "a" (which is angle APD) + BPC = 180 etc, is this the right track?

Edit : i know the picture is small - but if you click on it, you can see it more clearly
the general idea is right..
angle APD+angle BPC=180
similarly angle BPC+ and angle CPd= 180
Can you see what to do next?
To show that angle APD=angle CPd
4. Basically yes. If you look at two angles on line 2 and the same on line 1 you can get a pair of simultaneous equations:

After that, it's merely a case of solving those and reaching the conclusion.
5. (Original post by generalebriety)
That depends what you're allowed to assume here. Most schools would allow you to write down without proof (because it's fairly 'obvious') that angle BPA = angle CPD - if you're not allowed to write that, you might not be allowed to write that angle BPA + angle APD = 180 degrees. Nonetheless, if you know that you are allowed to write that, it's the right way forward.

Otherwise: can you tell us what exactly you've been taught already, so that we can see how to help you?
Its the first lesson of applied maths at uni,

We have been learning about euclids 5th axiom before now,

the exact question is "for the figure below show that if angle BPA has measure 'theta' then angle CPD has measure 'theta'
6. everyone ignore me i'm being stupid , i might need your help late though
7. (Original post by Hrov)
I have tried to do this but i just cant see how.
show that if Angle BPA has measue "a" then angle CPD has measure "a"
I have written equations such as "a" (which is angle APD) + BPC = 180 etc, is this the right track?

Edit : i know the picture is small - but if you click on it, you can see it more clearly
well they are vertically opposite angles.... so they are equal....
but in case you are not allowed without proof....
BPA+APD = 180
CPD+APD = 180
and subtract the two equations....
8. (Original post by Hrov)
Its the first lesson of applied maths at uni,

We have been learning about euclids 5th axiom before now,

the exact question is "for the figure below show that if angle BPA has measure 'theta' then angle CPD has measure 'theta'
Oh. Well, you're going to have to tell us what axioms you're working from. Otherwise we'll never know.
9. (Original post by generalebriety)
Oh. Well, you're going to have to tell us what axioms you're working from. Otherwise we'll never know.
im not sure but i think that we can only assume that a straight line is 180 degrees, and that if 2 parallel line bisect the same line, then certain angles will have to be the same to ensure that the lineS never meet, (PARALLEL)

. Can you help me with this i dont actually know where to start. (i tried to extend lines etc but i cant see what to do)

Show that if line1 is parrallel to line2 then a = b+c - 180
10. Extend line 1 and the diagonal line forming angle a so that they meet. You should know that the acute angle they meet in is a, and the other two in that triangle are 180-b and 180-c. But angles in a triangle need to add up to 180...
11. (Original post by generalebriety)
Extend line 1 and the diagonal line forming angle a so that they meet. You should know that the acute angle they meet in is a, and the other two in that triangle are 180-b and 180-c. But angles in a triangle need to add up to 180...
thanks a lot, i would rep you but it is worthless
Is there a quick way to prove that the acute angle is "a"? (just to be safe)
12. (Original post by Hrov)
thanks a lot, i would rep you but it is worthless
Is there a quick way to prove that the acute angle is "a"? (just to be safe)
I don't know, you still haven't told me what axioms you're using, so really I'm just guessing. And if you don't know what axioms you're using then so are you. But if the guesses you made a couple of posts ago are correct, then it's because line 1 and line 2 are parallel and cut the same line.

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Updated: October 11, 2009
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