Triangle
A triangle is
a figure formed when three
noncollinear points are
connected by segments.
Each
pair of segments forms an angle of the triangle. The vertex of
each angle is a vertex of the
triangle.
The sum of the measures of the angles of a triangle
is 180.
Area of a triangle
When you know the lenght of the base and the height, you can use the formula:
Area=·b·h, where b is the base and h is the height
Find the area of an acute triangle with a base of 15 inches and a height of 6 inches. 

Area=
·b·h
Area=
·(15 in)·(6 in)
Area=
·90 in
^{2}
Area=45 in
^{2}
Area of a triangle (Heron's Formula)
Heron's formula gives the area in terms of the three sides of the triangle:
Suppose we know the values of the three sides
a, b and
c of the triangle.
If
s is the semiperimeter of the triangle, that is,
s =
, then: