Difference between revisions of "Shoelace Theorem"
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==Proof== | ==Proof== | ||
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| + | == Problems == | ||
| + | === Introductory === | ||
| + | In right triangle <math>ABC</math>, we have <math>\angle ACB=90^{\circ}</math>, <math>AC=2</math>, and <math>BC=3</math>. [[Medians]] <math>AD</math> and <math>BE</math> are drawn to sides <math>BC</math> and <math>AC</math>, respectively. <math>AD</math> and <math>BE</math> intersect at point <math>F</math>. Find the area of <math>\triangle ABF</math>. | ||
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{{stub}} | {{stub}} | ||
Revision as of 10:46, 3 May 2009
The Shoelace Theorem is a nifty formula for finding the area of a polygon given the coordinates of its vertices.
Contents
Theorem
Suppose the polygon 
has vertices 
, 
, ... , 
, listed in clockwise order. Then area of is
![\[\dfrac{1}{2} |(a_1b_2 + a_2b_3 + \cdots + a_nb_1) - (b_1a_2 + b_2a_3 + \cdots + b_na_1)|\]](http://latex.artofproblemsolving.com/9/f/5/9f5392e8f69d97540c2fad3437685d2a8c6c19cb.png)
The Shoelace Theorem gets its name because if one lists the the coordinates in a column,
and marks the pairs of coordinates to be multiplied, the resulting image looks like laced-up shoes.
Proof
Problems
Introductory
In right triangle 
, we have 
, 
, and 
. Medians 
and 
are drawn to sides 
and 
, respectively. and intersect at point 
. Find the area of 
.
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