Difference between revisions of "1964 IMO Problems/Problem 6"

(Solution)
(Solution)
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<math>|CC_{2}|=3|D_{0}C_{2}|</math>
 
<math>|CC_{2}|=3|D_{0}C_{2}|</math>
  
Since <math>\Delta D_{0}A_{2}A_{1}\sim \Delta AA_{2}A_{1}</math>, then $|AA_{2}|=|DD_{0}| \frac{|AA_{2}|}{|D_{0}A_{2}|}
+
Since <math>\Delta D_{0}A_{2}A_{1}\sim \Delta AA_{2}A_{1}</math>, then <math>|AA_{2}|=|DD_{0}| \frac{|AA_{2}|}{|D_{0}A_{2}|}</math>
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Revision as of 22:47, 16 November 2023

Problem

In tetrahedron $ABCD$, vertex $D$ is connected with $D_0$, the centroid of $\triangle ABC$. Lines parallel to $DD_0$ are drawn through $A,B$ and $C$. These lines intersect the planes $BCD, CAD$ and $ABD$ in points $A_1, B_1,$ and $C_1$, respectively. Prove that the volume of $ABCD$ is one third the volume of $A_1B_1C_1D_0$. Is the result true if point $D_o$ is selected anywhere within $\triangle ABC$?

Solution

Let $A_{2}$ be the point where line $AD_{0}$ intersects line $BC$

Let $B_{2}$ be the point where line $BD_{0}$ intersects line $AC$

Let $C_{2}$ be the point where line $CD_{0}$ intersects line $AB$

From centroid properties we have:

$|AA_{2}|=3|D_{0}A_{2}|$

$|BB_{2}|=3|D_{0}B_{2}|$

$|CC_{2}|=3|D_{0}C_{2}|$

Since $\Delta D_{0}A_{2}A_{1}\sim \Delta AA_{2}A_{1}$, then $|AA_{2}|=|DD_{0}| \frac{|AA_{2}|}{|D_{0}A_{2}|}$


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See Also

1964 IMO (Problems) • Resources
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Problem 5
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All IMO Problems and Solutions