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GPREP Co-ordinate geometry

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by sudhir3127 » Fri Aug 01, 2008 7:47 am
Use the Area of triangle formula

1/2 mod( ( X1-X2)* (Y2-Y3) - (Y1-Y2)( Y2-Y3))

there fore

1/2 mod ( -4* (-4) - (-3)*3 )

1/2 mod (25) = 12.5

hope its clear...
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by zagcollins » Fri Aug 01, 2008 7:57 am
didnt get ya..is this the distance formula that you have used??
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by sudhir3127 » Fri Aug 01, 2008 8:00 am
Thats actually the formula for area of the triangle when 3 points are given in cood geometry,

( 0,3) is (X1,Y1)
(4,0) is (X2,Y2)
(7,4) is ( X3,Y3)

You need to remember the formula..

do let me know if u are still in doubt
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by nadontheway » Fri Aug 01, 2008 8:22 am
pls can u check the end of your formula. something seems incorrect. thx.
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by pepeprepa » Fri Aug 01, 2008 8:24 am
Another way.

The are of the triangle we want is in a rectangle with is 7 length and 4 wide (so this rectangle has an area of 28).
Now let's subtract to this area the 3 right triangles.
Triangle OPQ: (4*3)/2=6
2nd triangle: (1*7)/2=3,5
3rd triangle: (3*4)/2=6

The sum of the area of these 3 triangles is 15,5
We subtract it to the area of the rectangle and we have the area of PQR:
28-15,5=12,5
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by sudhir3127 » Fri Aug 01, 2008 8:25 am
sorrie its a typo....

1/2 mod( ( X1-X2)* (Y2-Y3) - (Y1-Y2)( X2-X3))

thanks for pointing out...

sorry Zag abt it ...
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by pepeprepa » Fri Aug 01, 2008 8:33 am
I don't think it is a paramount point, but what does "mod" mean in your formula?
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by sudhir3127 » Fri Aug 01, 2008 8:48 am
Mod means Absolute ..
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by zagcollins » Fri Aug 01, 2008 7:25 pm
i get it now, sudhir...thanks....
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by pepeprepa » Sat Aug 02, 2008 12:38 am
Okay thanks Sudhir... I didn't know, I thought Absolute was written "Abs"
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