Explanation:
Triangle
A triangle is one of the basic shapes of geometry: a polygon with three corners or vertices and three sides or edges which are line segments. A triangle with
vertices A, B, and C is denoted 
ABC.
Computing the area of a triangle
Using coordinates
If vertex A
is located at the origin (0, 0) of a Cartesian coordinate system and the coordinates of the
other two vertices are given by B = (xB, yB)
and C = (xC, yC), then the
area can be computed as � times the absolute value of the determinant
For three
general vertices, the equation is:
In three
dimensions, the area of a general triangle {A = (xA, yA, zA),
B = (xB, yB, zB)
and C = (xC, yC, zC)}
is the Pythagorean sum of the areas of the
respective projections on the three principal planes (i.e. x = 0, y = 0 and z = 0):
(Our solved example in mathguru.com uses
this concept)
http://en.wikipedia.org/wiki/Triangle
The
above explanation is copied from Wikipedia, the free encyclopedia and is
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License.