geometryarea

edge triangle

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#include <codecogs/geometry/area/edge_triangle.h>

using namespace Geometry::Area;

double edge_triangle (double a, double b, double c, double h)[inline]
Computes the area of a trapezium within a triangle with a fixed edge.
Click for details on using CodeCogs in ExcelReal cc_edge_triangle (Real a, Real b, Real c, Real h)
This function is available as a Microsoft Excel add-in.

Function Documentation

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doubleedge_triangledoublea
doubleb
doublec
doubleh )[inline]
This module computes the area of the trapezium formed between a triangle with a fixed edge on a reference line and a line found at a given distance distance from this reference line.

This situation is described by the following image. The area which we want to compute is that of the filled trapezium [BB_1C_1C].

1/edge_triangle-746.jpg
Solution

Let \mathrm{xOy} be an orthogonal coordinate system and let \triangle ABC be an arbitrary triangle so that BC \subset \mathrm{Ox} and
(1)
\displaystyle BC = a \qquad AC = b \qquad AB = c
where a, b, c \in \mathbb{R}_+^* are fixed numbers. Also let d  \parallel \mathrm{Ox} so that the distance between the line d and \mathrm{Ox} equals h \in \mathbb{R}_+ and AB \cap d = \{B_1\} , AC \cap d = \{C_1\} .

Obviously \triangle AB_1C_1 \sim \triangle ABC which implies:

(2)
\displaystyle \frac{B_1C_1}{BC} = \frac{H - h}{H} \qquad \Rightarrow \qquad B_1C_1 = a \left( 1 - \frac{h}{H} \right )

where H is the height corresponding to vertex A.

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Example:
#include <codecogs/geometry/area/edge_triangle.h>
#include <stdio.h>
 
int main()
{
  // the lengths of the sides
  double a = 3.3, b = 4.5, c = 5.4;
 
  // display the lengths of the sides
  printf("a = %.1lf\nb = %.1lf\nc = %.1lf\n\n", a, b, c);
 
  // display the area for different values of h
  for (double h = 0.1; h < 1.09; h += 0.1)
    printf("h = %.1lf   Area = %.2lf\n", h, 
    Geometry::Area::edge_triangle(a, b, c, h));
 
  return 0;
}

Output:
a = 3.3
b = 4.5
c = 5.4
 
h = 0.1   Area = 0.33
h = 0.2   Area = 0.65
h = 0.3   Area = 0.96
h = 0.4   Area = 1.26
h = 0.5   Area = 1.56
h = 0.6   Area = 1.85
h = 0.7   Area = 2.13
h = 0.8   Area = 2.40
h = 0.9   Area = 2.67
h = 1.0   Area = 2.93
Parameters:
afirst side of the triangle (BC)
bsecond side of the triangle (AC)
cthird side of the triangle (AB)
hthe distance between line d and \mathrm{Ox}
Returns:
The value of the desired area.
Note:
The values of the sides must satisfy the triangle inequality.
Authors:
Eduard Bentea (September 2006)
Source Code:
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Last Modified: 29 Oct 07 @ 09:35     Page Rendered: 2008-05-09 16:02:44

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