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Teachers' Lounge Discussion: Explaining angle construction

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From: Loyd

To: Teacher2Teacher Public Discussion
Date: 2011010314:02:00
Subject: Re: 120 degree angle contruction?

On 2007022717:17:31, emily wrote: > >I have a geometry project due, and I have to construct a 120 degree >angle only using a straightedge and a compass. can anyone help me?? > Go to this site and see the method for constructing a 30 degree angle. Add that to a 90 degree angle (by constructing a square) and you have a 120 degree angle. http://www.mathopenref.com/constangle30.html When I first saw this problem, I thought of my high school geometry when some of my friends tried to trisect an angle with only a staightedge and compass. So, my first thought was it would be impossible. But for a 30 degree angle, a neat construction is shown on the above web site that uses only a straightedge and compass.

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