Solve it anyway!

Geometry Level 4

In the above given figure determine the length of the blue line EC


The figure is not drawn to scale . Can you solve this without using coordinates?


The answer is 18.

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2 solutions

Once you observe the cyclic quadrilateral, you can apply the formula

A E C E = A B C D × A D C B . \frac{ AE } { CE } = \frac{ AB}{CD} \times \frac{AD}{CB}.

Do you see why that is true? You alluded to it in your approach, but I think it's obscured in all of the calculations that you did after that.

Calvin Lin Staff - 4 years, 6 months ago

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Oh ...I agree

Vishwash Kumar ΓΞΩ - 4 years, 6 months ago

I used the technique by using the properties of similar triangles in triangle AED and BEC but didn't use it in the other pair of triangles that is AEB and triangle DEC . to get the formula given by you . That was my mistake although now I have rectified that thanks .

Vishwash Kumar ΓΞΩ - 4 years, 6 months ago
Ayush G Rai
Nov 21, 2016

It will be better if you delete yourcomment from my question

Vishwash Kumar ΓΞΩ - 4 years, 6 months ago

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ok.i have deleted

Ayush G Rai - 4 years, 6 months ago

I too can but I willn't

Vishwash Kumar ΓΞΩ - 4 years, 6 months ago

@Ayush Rai

Vishwash Kumar ΓΞΩ - 4 years, 6 months ago

good solution i did it the same way

A Former Brilliant Member - 4 years, 6 months ago

Once you observe the cyclic quadrilateral, a better formula to apply is

A E C E = A B C D × A D C B . \frac{ AE } { CE } = \frac{ AB}{CD} \times \frac{AD}{CB}.

This avoids relying on the condition that the angles are right. It follows from the area observation applied to other triangles.

Calvin Lin Staff - 4 years, 6 months ago

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