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.
The sum of the lengths of any two sides of a triangle must be greater than the third side. That is:
a + b > c
a + c > b
b + c > a
The subtraction of the lengths of any two sides of a triangle must be smaller than the third side.
Triangles can be classified by:
Their sides:
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Equilateral
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Isosceles
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Scalene
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All three sides have equal lengths
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Exactly two equal sides
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All sides have different lengths
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Their angles:
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Acute
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Right
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Obtuse
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All interior angles are acute (<90º)
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One angle is a right angle (90º)
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One angle is obtuse (>90º)
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Area of a triangle
There are several ways to compute the area of a triangle:
1.
When you know the lenght of the base and the height, you can use the formula:
2. Another is Heron's formula which 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 = (a + b + c)/2, then:
