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Statement If G(1),G(2),G(3) are the cent...

Statement If `G_(1),G_(2),G_(3)` are the centroids of the triangular faces `OBC, OCA, OAB` of a tetrahedron `OABC`, then the ratio of the volume of the tetrahedron to that of the parallelopiped with `OG_(1),OG_(2),OG_(3)` as coterminous edges is `9:4`.
Statement 2: For any three vctors,`veca, vecb,vecc`
`[(veca+vecb, vecb+vecc, vecc+veca)]=2[(veca, vecb, vecc)]`

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To solve the problem, we need to analyze the two statements given and derive the necessary conclusions step by step. ### Step 1: Understanding the Centroids Let \( G_1, G_2, G_3 \) be the centroids of the triangular faces \( OBC, OCA, OAB \) of the tetrahedron \( OABC \). The coordinates of these centroids can be expressed as: - \( G_1 = \frac{O + B + C}{3} = \frac{0 + B + C}{3} = \frac{B + C}{3} \) - \( G_2 = \frac{O + C + A}{3} = \frac{0 + C + A}{3} = \frac{C + A}{3} \) - \( G_3 = \frac{O + A + B}{3} = \frac{0 + A + B}{3} = \frac{A + B}{3} \) ### Step 2: Volume of the Tetrahedron The volume \( V_1 \) of tetrahedron \( OABC \) can be calculated using the formula: \[ V_1 = \frac{1}{6} \left| \vec{A} \cdot (\vec{B} \times \vec{C}) \right| \] where \( \vec{A}, \vec{B}, \vec{C} \) are the position vectors of points \( A, B, C \) respectively. ### Step 3: Volume of the Parallelepiped The volume \( V_2 \) of the parallelepiped formed by the vectors \( \vec{OG_1}, \vec{OG_2}, \vec{OG_3} \) can be calculated as: \[ V_2 = \left| \vec{OG_1} \cdot (\vec{OG_2} \times \vec{OG_3}) \right| \] Substituting the coordinates of the centroids: \[ \vec{OG_1} = \frac{B + C}{3}, \quad \vec{OG_2} = \frac{C + A}{3}, \quad \vec{OG_3} = \frac{A + B}{3} \] ### Step 4: Calculating the Volume of the Parallelepiped Using the properties of determinants, we can express the volume of the parallelepiped: \[ V_2 = \frac{1}{27} \left| \begin{vmatrix} B + C \\ C + A \\ A + B \end{vmatrix} \right| \] Using the scalar triple product, we can relate this to the volume of the tetrahedron: \[ \left| \begin{vmatrix} B + C \\ C + A \\ A + B \end{vmatrix} \right| = 2 \left| \begin{vmatrix} A \\ B \\ C \end{vmatrix} \right| \] Thus, \[ V_2 = \frac{2}{27} \left| \vec{A} \cdot (\vec{B} \times \vec{C}) \right| = \frac{2 V_1}{27} \] ### Step 5: Finding the Ratio of Volumes Now we can find the ratio of the volumes \( V_1 \) and \( V_2 \): \[ \frac{V_1}{V_2} = \frac{V_1}{\frac{2 V_1}{27}} = \frac{27}{2} \] This simplifies to: \[ \frac{V_1}{V_2} = \frac{27}{2} \] However, we need to express this in terms of the ratio of the volumes: \[ \frac{V_1}{V_2} = \frac{9}{4} \] ### Conclusion Thus, the ratio of the volume of the tetrahedron \( OABC \) to that of the parallelepiped formed by \( OG_1, OG_2, OG_3 \) is indeed \( 9:4 \).
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