# Is this possible?

• Mar 16th 2006, 12:08 AM
jacs
Is this possible?
Is it possible to prove a triangle ABC is isosceles, given only that Ậ = 50º

???????

thanks

• Mar 16th 2006, 03:45 AM
CaptainBlack
Quote:

Originally Posted by jacs
Is it possible to prove a triangle ABC is isosceles, given only that Ậ = 50º

???????

thanks

No. Since an isosceles triangle must have two equal angles, but the only
constraint on a general triangle is that the angle sum is 180 degrees.
So a triangle with an angle of 50 degrees could have its other angles as
60 and 70 degrees and hence need not be isosceles.

RonL
• Mar 16th 2006, 03:50 AM
jacs
thanks for that, that is pretty much what i thought too, but teacher insists it can be done.

Should get his working tomorrow, which will prove interesting. I guess he must know some alternate universe geometry that we don't.

Or perhaps he just gave us the wrong info, (wouldnt be the first time)
lol

i will post his answer for a laugh, see what he manages to come up with

thanks CaptainBlack
• Mar 16th 2006, 05:40 AM
c_323_h
how come the other two angles couldn't be 65 degrees?
• Mar 16th 2006, 07:19 AM
CaptainBlack
Quote:

Originally Posted by c_323_h
how come the other two angles couldn't be 65 degrees?

They could be, but you can't prove that they must be (at least not
without some additional conditions).

RonL
• Mar 16th 2006, 01:39 PM
ThePerfectHacker
Quote:

Originally Posted by jacs
thanks for that, that is pretty much what i thought too, but teacher insists it can be done.

Should get his working tomorrow, which will prove interesting. I guess he must know some alternate universe geometry that we don't.

Or perhaps he just gave us the wrong info, (wouldnt be the first time)
lol

i will post his answer for a laugh, see what he manages to come up with

thanks CaptainBlack

Perhaps your teacher thinks in Lobachevskian Space?
(No idea how to spell it)
• Mar 16th 2006, 01:53 PM
CaptainBlack
Quote:

Originally Posted by ThePerfectHacker
Perhaps your teacher thinks in Lobachevskian Space?
(No idea how to spell it)

Still not a theorem in hyperbolic or elliptic geometries

RonL
• Mar 18th 2006, 03:55 AM
jacs
Well, it turns out, ooopps surprise, he forgot a vital peice of information, like the second angle is also 50.

So that solves that little quandary, thanks for you input everyone.

jacs