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Geometry Difficulty 6.5 National Olympiad Prove it North Macedonia

Let HH be the orthocenter of the triangle ABC\triangle ABC and A1A_1, B1B_1, C1C_1 be the feet of the altitudes from AA, BB, CC respectively.
Find AHHA1BHHB1CHHC1\frac{\overline{AH}}{HA_1} \cdot \frac{\overline{BH}}{HB_1} \cdot \frac{\overline{CH}}{HC_1} if AHHA1+BHHB1+CHHC1=2008\frac{\overline{AH}}{HA_1} + \frac{\overline{BH}}{HB_1} + \frac{\overline{CH}}{HC_1} = 2008.

Solution

We have
AHHA1+1=AHHA1+HA1HA1=AA1HA1=PABCPHBC. \frac{\overline{AH}}{HA_1} + 1 = \frac{\overline{AH}}{HA_1} + \frac{\overline{HA_1}}{HA_1} = \frac{\overline{AA_1}}{HA_1} = \frac{P_{\triangle ABC}}{P_{\triangle HBC}}.
Similarly, BHHB1+1=PHBCPHCA\frac{\overline{BH}}{HB_1} + 1 = \frac{P_{\triangle HBC}}{P_{\triangle HCA}} and CHHC1+1=PHBCPHAB\frac{\overline{CH}}{HC_1} + 1 = \frac{P_{\triangle HBC}}{P_{\triangle HAB}}. If x=PHBCx = P_{\triangle HBC}, y=PHCAy = P_{\triangle HCA}, z=PHABz = P_{\triangle HAB}, then

PABC=x+y+zP_{\triangle ABC} = x + y + z. Now AHHA1+BHHB1+CHHC1=2008\frac{\overline{AH}}{HA_1} + \frac{\overline{BH}}{HB_1} + \frac{\overline{CH}}{HC_1} = 2008 is equivalent to
x+y+zx1+x+y+zy1+x+y+zz1=2008, \frac{x+y+z}{x} - 1 + \frac{x+y+z}{y} - 1 + \frac{x+y+z}{z} - 1 = 2008,
from where (x+y+z)(yz+xz+xy)=2011xyz(x+y+z)(yz+xz+xy) = 2011xyz.
Finally
(x+y+zx1)(x+y+zy1)(x+y+zz1)=y+zxx+zyx+yz=(y+z)(x+z)(x+y)xyz==(x+y+z)(yz+xz+xy)xyzxyz=2011xyzxyzxyz=2010 \begin{aligned} & \left(\frac{x+y+z}{x}-1\right) \cdot \left(\frac{x+y+z}{y}-1\right) \cdot \left(\frac{x+y+z}{z}-1\right) = \frac{y+z}{x} \cdot \frac{x+z}{y} \cdot \frac{x+y}{z} = \frac{(y+z)(x+z)(x+y)}{xyz} = \\ & = \frac{(x+y+z)(yz+xz+xy)-xyz}{xyz} = \frac{2011xyz-xyz}{xyz} = 2010 \end{aligned}

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Source: MathNet, licensed CC-BY-4.0. Statement reproduced verbatim; metadata (topic, difficulty) added by this project.