Moment of Inertia About y-Axis

I_{y} = - \frac{1}{12} \cdot \sum_{i = 1}^{n} ({z_{i}}^{3} + {z_{i}}^{2} \cdot z_{i - 1} + z_{i} \cdot {z_{i - 1}}^{2} + {z_{i - 1}}^{3}) \cdot (y_{i} - y_{i - 1})

y	y-coordinate of the polygon point
z	z-coordinate of the polygon point

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