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Teachers' Lounge Discussion: Coordinate proofs

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From: Alex Contreras

To: Teacher2Teacher Public Discussion
Date: 2007031315:28:14
Subject: Re: Coordinate Proofs

**quote** Please help me! How can I write a coordinate proof to show that the diagonals of a rectangle are congruent? Also, How can I find the perimeter and area of Triangle ABC if A= (-4,3) B=(11,3) C=(11,11) Well, For the perimeter of Triangle ABC if A,B, and C are as mentioned above, then one would use the distance formula for each side, or use it for only 2 sides and then use the pythagorean theorem for the last. The distance formula is squareroot( (x1-x2)^2 + (y1-y2) ) For example, finding the distance of AB would be: squareroot ( (-4 - 11)^2 + (3-3)^2 ) then to find the area, you would have to see what kind of triangle it is: if it is not scalene, you can do 1/2 bh if it IS scalene, then you use Heron's formula: S=(a+b+c)/2) semiperimeter of trianlge squareroot ( s*(s-a)*(s-b)*(s-c) ) and that will give you the exact area. i hope thats not too confusing. email me if you want anymore info. deltaepsylon REMOVE THIS@gmail.com

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