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1.3: Площині
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We consider an elemental triangular sector (Figure I.6) between $\theta$ and $\theta + \delta \theta$ . The "height" of the triangle is r and the "base" is $r \delta \theta$ . The horizonta...We consider an elemental triangular sector (Figure I.6) between $\theta$ and $\theta + \delta \theta$ . The "height" of the triangle is r and the "base" is $r \delta \theta$ . The horizontal distance of the centroid of the elemental sector from the origin (more correctly, from the "pole" of the polar coordinate system) is $\frac{2}{3} r \cos \theta$ . The first moment of area of the sector with respect to the $y$ axis is