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Moderator edit: This topic is for commentary pertaining to the tutorial:

http://mathhelpboards.com/math-notes-49/finding-area-triangle-formed-3-points-plane-2954.html

Hello, MarkFL!

Sorry, your formula doesn't work.

Try it for: $(0,0), (6,0), (0,4).$

The area should be $12.$

The formula that I saw derived years ago:

. . $A \;=\;\dfrac{1}{2}\begin{vmatrix}1&1&1 \\ x_1 & x_2 & x_3 \\ y_1 & y_2 & y_3 \end{vmatrix}$

where we take the absolute value of the determinant.

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