Is the information sufficient 9?

Geometry Level 3

In A B C \triangle ABC , A = 12 0 \angle A = 120^{\circ} , A B = 18 \overline{AB} = 18 and A C = 24 \overline{AC} = 24 . A \angle A has been trisected by segments A E \overline{AE} and A D \overline{AD} as shown in the figure above. If B E A D A E D C = m n \dfrac{ \overline{BE} \cdot \overline{AD} }{\overline{AE} \cdot \overline{DC}} = \dfrac{m}{n} , where m m and n n are coprime positive integers, what is the value of 2016 m + n \dfrac{2016}{m + n} ?


For more problems like this, try answering this set .


The answer is 288.

This section requires Javascript.
You are seeing this because something didn't load right. We suggest you, (a) try refreshing the page, (b) enabling javascript if it is disabled on your browser and, finally, (c) loading the non-javascript version of this page . We're sorry about the hassle.

3 solutions

Chew-Seong Cheong
Jun 29, 2017

Relevant wiki: Sine Rule (Law of Sines)

Q = B E A D A E D C Using sine rule = sin B A E sin C sin B sin D A C = sin 4 0 sin C sin B sin 4 0 = sin C sin B Using sine rule again = A B A C = 18 24 = 3 4 \begin{aligned} Q & = \frac {{\color{#3D99F6}\overline{BE}}\cdot{\color{#D61F06}\overline{AD}}}{{\color{#3D99F6}\overline{AE}} \cdot {\color{#D61F06} \overline{DC}}} & \small \color{#3D99F6} \text{Using sine rule} \\ & = \frac {{\color{#3D99F6}\sin \angle BAE}\cdot{\color{#D61F06}\sin \angle C}}{{\color{#3D99F6}\sin \angle B}\cdot{\color{#D61F06}\sin \angle DAC}} \\ & = \frac {\sin 40^\circ\cdot\sin \angle C}{\sin \angle B\cdot \sin 40^\circ} \\ & = \frac {\sin \angle C}{\sin \angle B} & \small \color{#3D99F6} \text{Using sine rule again} \\ & = \frac {\overline{AB}} {\overline{AC}} = \frac {18}{24} = \frac 34 \end{aligned}

2016 m + n = 2016 3 + 4 = 288 \implies \dfrac {2016}{m+n} = \dfrac {2016}{3+4} = \boxed{288}

Sir, do you have any other alternative solutions except for that sir? :D (But this solution is really good. :) )

Christian Daang - 3 years, 11 months ago
Kushal Bose
Jun 30, 2017

Consider the Δ A B D \Delta ABD where AE is the bisector of B A D \angle BAD .So, applying bisector theorem

A B A D = B E E D \dfrac{AB}{AD}=\dfrac{BE}{ED} ..............................Equation(1)

Consider Δ A E C \Delta AEC where AD is the bisector of E A C \angle EAC .Again applying the theorem

A C A E = C D E D \dfrac{AC}{AE}=\dfrac{CD}{ED} ..............................Equation(2)

Now dividing equation (1) by equation (2):

A B A C . A E A D = B E C D B E . A D C D . A E = A B A C = 18 24 = 3 4 \dfrac{AB}{AC}. \dfrac{AE}{AD}=\dfrac{BE}{CD}\\ \dfrac{BE.AD}{CD.AE}=\dfrac{AB}{AC}=\dfrac{18}{24}=\dfrac{3}{4}

Christian Daang
Jun 30, 2017

By Using the Bisector Theorem in Δ A B D \Delta ABD

18 B E = A D D E B E = 18 D E A D ( 1 ) \implies \dfrac{18}{\overline{BE}} = \dfrac{\overline{AD}}{\overline{DE}} \\ \implies \overline{BE} = \dfrac{18\overline{DE}}{\overline{AD}} \rightarrow (1)

By Using the Bisector Theorem in Δ A E C \Delta AEC

A E E D = 24 D C D E = A E D C 24 ( 2 ) \implies \dfrac{\overline{AE}}{\overline{ED}} = \dfrac{24}{\overline{DC}} \\ \implies \overline{DE} = \dfrac{\overline{AE} \cdot \overline{DC}}{24} \rightarrow (2)

Combining ( 1 ) (1) and ( 2 ) (2) ,

B E = 18 ( A E D C 24 ) A D B E A D A E D C = 18 24 = 3 4 = m n 2016 m + n = 288 \implies \overline{BE} = \dfrac{18 \left( \dfrac{\overline{AE} \cdot \overline{DC}}{24} \right)}{\overline{AD}} \\ \therefore \dfrac{ \overline{BE} \cdot \overline{AD} }{\overline{AE} \cdot \overline{DC}} = \dfrac{18}{24} = \dfrac{3}{4} = \dfrac{m}{n} \\ \implies \boxed{\dfrac{2016}{m + n} = 288 }

0 pending reports

×

Problem Loading...

Note Loading...

Set Loading...