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This online calculator calculates the area of a polygon given lengths of polygon sides and diagonals, which split the polygon into non-overlapping triangles.
As shown in the picture, you can sum areas of triangles ABD, BCD, and ADE to calculate the polygon ABCDE area. To do this, you need lengths of diagonals: BD and AD, but this is all you need. The thing is that you can calculate the area of any triangle given only its side lengths.
This is useful for apartment renovation, for example, cause at home, it is easier to measure lengths than to measure angles.
To calculate the polygon area, you measure side lengths, put them into the table below, then split the polygon into non-overlapping triangles, measure needed diagonals, put them into the table, and you're done.
The calculator computes the total area and also outputs all triangles it is used for calculation. "Error" field gives you a hint which vertex still isn’t part of any triangle.
The input table is filled with data for the picture; press the "Clear table" button to clear it.