Explanation:
In an isosceles triangle, two sides are equal in
length. An isosceles triangle also has
two angles of the same measure; namely, the angles opposite to the two sides of
the same length; this fact is the content of the Isosceles triangle theorem.
Some mathematicians define an isosceles triangle to have exactly two equal
sides, whereas others define an isosceles triangle as one with at least two equal sides.^{[3]} The latter definition would
make all equilateral triangles isosceles triangles.
Computing
the area of a triangle
Using Heron's formula
The shape of the triangle is determined by the lengths of the
sides alone. Therefore the area can also be derived from the lengths of the
sides. By Heron's formula:
where is
the semi perimeter, or
half of the triangle's perimeter. (Our solved example in mathguru.com uses this concept)
Three equivalent ways of writing Heron's formula are
http://en.wikipedia.org/wiki/Triangle
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