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Baltic Way 1995 · Problem 17

Geometry

Prove that there exists a number α\alpha such that for any triangle ABCA B C the inequality

max⁡(hA,hB,hC)≤α⋅min⁡(mA,mB,mC)\max \left(h_{A}, h_{B}, h_{C}\right) \leq \alpha \cdot \min \left(m_{A}, m_{B}, m_{C}\right)

holds, where hA,hB,hCh_{A}, h_{B}, h_{C} denote the lengths of the altitudes and mA,mB,mCm_{A}, m_{B}, m_{C} denote the lengths of the medians. Find the smallest possible value of α\alpha.

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Topics

Geometric inequalities · Triangles and centers

Solutions

Solution

Solution:

Let h=max⁡(hA,hB,hC)h = \max \left(h_{A}, h_{B}, h_{C}\right) and m=min⁡(mA,mB,mC)m = \min \left(m_{A}, m_{B}, m_{C}\right). If the longest height and the shortest median are drawn from the same vertex, then obviously h≤mh \leq m.

Now let the longest height and shortest median be ADA D and BEB E, respectively, with ∣AD∣=h|A D| = h and ∣BE∣=m|B E| = m. Let FF be the point on the line BCB C such that EFE F is parallel to ADA D. Then m=∣EB∣≥∣EF∣=h2m = |E B| \geq |E F| = \frac{h}{2}, whence h≤2mh \leq 2 m.

For an example with h=2mh = 2 m, consider a triangle where DD lies on the ray CBC B with ∣CB∣=∣BD∣|C B| = |B D|. Hence the smallest such value is α=2\alpha = 2.

Contest context

Results from Baltic Way 1995

9 teams

Mean score
2.0 / 5
Scores of 4 or 5
3 / 9
Estonia
0 / 5

Score distribution

04
11
21
30
40
53
All team scores
TeamScore
Poland2 / 5
Latvia0 / 5
Sweden5 / 5
Lithuania5 / 5
Denmark5 / 5
Finland0 / 5
St. Petersburg0 / 5
Estonia0 / 5
Iceland1 / 5