Chapter 20: Problem 7
Any one-point set as well as any segment in the Euclidean plane have vanishing area.
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Chapter 20: Problem 7
Any one-point set as well as any segment in the Euclidean plane have vanishing area.
These are the key concepts you need to understand to accurately answer the question.
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Assume that diagonals of a nondegenerate quadrangle ABCD intersect at point M. Show that $$\operatorname{area}(\boldsymbol{\Delta} A B M) \cdot \operatorname{area}(\boldsymbol{\Delta} C D M)=\operatorname{area}(\boldsymbol{\Delta} B C M) \cdot \operatorname{area}(\boldsymbol{\Delta} D A M)$$
Assume \(\square A B C D\) and \(\square A B^{\prime} C^{\prime} D^{\prime}\) are two parallelograms such that \(B^{\prime} \in[B C]\) and \(D \in\) \(\in\left[C^{\prime} D^{\prime}\right] .\) Show that $$\operatorname{area}(\mathbf{\square} A B C D)=\operatorname{area}\left(\mathbf{\square} A B^{\prime} C^{\prime}D^{\prime}\right)$$
Let \(r\) be the inradius of \(\triangle A B C\) and \(p\) be its semiperimeter; that is, \(p=\frac{1}{2} \cdot(A B+B C+C A) .\) Show that $$\operatorname{area}(\boldsymbol{\Delta} A B C)=p \cdot r$$
Let \(A B C\) be a nondegenerate triangle. Suppose its cevians \(\left[A A^{\prime}\right],\left[B B^{\prime}\right]\) and \(\left[C C^{\prime}\right]\) intersect at one point \(X .\) Show that $$\begin{array}{l} \frac{\operatorname{area}(\boldsymbol{\Delta} A B X)}{\operatorname{area}(\boldsymbol{\Delta} B C X)}=\frac{A B^{\prime}}{B^{\prime} C} \\\\\frac{\operatorname{area}(\boldsymbol{\Delta} B C X)}{\operatorname{area}(\boldsymbol{\Delta} C A X)}=\frac{B C^{\prime}}{C^{\prime} A}, \\ \frac{\operatorname{area}(\boldsymbol{\Delta} C A X)}{\operatorname{area}(\boldsymbol{\Delta} A B X)}=\frac{C A^{\prime}}{A^{\prime} B} .\end{array}$$ Conclude that $$\frac{A B^{\prime} \cdot C A^{\prime} \cdot B C^{\prime}}{B^{\prime} C \cdot A^{\prime} B \cdot C^{\prime} A}=1$$
Show that any solid triangle is convex; that is, for any pair of points \(X, Y \in \triangle A B C,\) then the line segment \([X Y]\) lies in \(\triangle A B C\).
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