This diagram shows a three dimensional graph, with three axes. The x axis is labeled x subscript one, the y axis is labeled x subscript two, and the z axis is labeled x subscript three. A green dot that exists in the area bounded by the x subscript one axis, x subscript two axis, and a line that connects the two axes is labeled lowercase n subscript three, sigma. A green arrow pointing from a location next to the green dot in the same region points to negative k, which is also in green. In the location bounded by the axes x subscript one and x subscript three, along with the line that connects the two axes, there is a magenta arrow that points to a magenta negative lowercase j. Next to this arrow, also in magenta, is another dot. This dot is labeled lowercase n subscript two, sigma. In a third region that is bounded by x subscript two, x subscript three, and the line that connects the two axis is a blue arrow that points from this region to negative lowercase i, also in blue. A blue dot in the same region is labeled by a lowercase n subscript one, sigma. In the fourth region, the one bounded by the three lines that connect the axes, an arrow pointing from a location on this region points to an equation, lowercase n equals lowercase bold n equals lowercase n subscript one times lowercase bold i, plus lowercase n subscript two times lowercase bold j, plus lowercase n subscript three times lowercase bold k. This equation and the arrow pointing to it are labeled in red. In this same region, there is a red dot that is labeled by the term area sigma, also in red.
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