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Q&A #3945

Teachers' Lounge Discussion: Coordinate proofs

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From: Alex Contreras <deltaepsylon@gmail.com>
To: Teacher2Teacher Public Discussion
Date: 2007031314:28:14
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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