Distance between the Points

Geometry Level 4

Consider a semicircle of radius 1 on the diameter A B AB where the center is O O .

A point C C divides A O AO in the ratio 2 : 1 2:1 .

A line that is perpendicular to A O AO passing through C C cuts the semicircle at E E .

Another line O L OL passing through O O and is perpendicular to A E AE intersects C E CE at H H .

Find the value of E H EH .

1 3 \frac{1}{\sqrt{3}} 1 2 \frac{1}{\sqrt{2}} 1 5 \frac{1}{\sqrt{5}} 1 5 2 \frac{1-\sqrt{5}}{2}

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3 solutions

Benny Joseph
Nov 6, 2016

Ayush G Rai
Nov 9, 2016

We first get A C = 2 3 , C O = 1 3 AC=\frac{2}{3},CO=\frac{1}{3} and E C = 2 2 3 EC=\frac{2\sqrt2}{3} using Pythagoras Theorem on E C O . \triangle ECO.
We observe that A L = L E AL=LE since A O E \triangle AOE is isosceles and C H = 2 2 3 E H 3 . CH=\frac{2\sqrt2-3EH}{3}.
We apply Menelaus Theorem for E C A \triangle ECA with L O LO as the transversal.
So, A O C O × C H E H × L E A L = 1 \dfrac{AO}{CO}\times\dfrac{CH}{EH}\times\dfrac{LE}{AL}=1 [ [ Actually it should be 1 -1 but it doesn't affect the problem as the minus sign is just to indicate that the point O O does not lie between A C AC ] . ].
1 1 3 × C H E H × L E A L = 1. \Rightarrow\dfrac{1}{\frac{1}{3}}\times \dfrac{CH}{EH}\times\dfrac{\cancel{LE}}{\cancel{AL}}=1.
C H E H = 1 3 . \Rightarrow \dfrac{CH}{EH}=\dfrac{1}{3}.
2 2 3 E H 3 E H = 1 3 . \Rightarrow \dfrac{2\sqrt2-3EH}{\cancel{3}EH}=\dfrac{1}{\cancel{3}}.
Therefore after solving we get E H = 1 2 . EH=\boxed{\dfrac{1}{\sqrt2}}.


Hey how was you able to make a cut ?

vishwash kumar - 4 years, 7 months ago

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latex thinking.\require{cancel} mention this at the beginning of your statement where u want to make the cut.then \cancel{3}.this will be represented as 3 . \cancel{3}.

Ayush G Rai - 4 years, 7 months ago

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