Area Of Triangle Problem

Geometry Level 4

Find The area of Δ J K L \Delta JKL . The number enclosed in figures are areas in square units


The answer is 144.

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3 solutions

Abhijeet Verma
Sep 5, 2015

The question can easily be solved using the similarity between the triangles. It can easily be deduced that F P C L a n d E P B K a r e p a r a l l e l o g r a m s F P = L C . . . . . . . ( 1 ) P E = B K . . . . . . . ( 2 ) A F P P C B D P E P C B t h e r e f o r e , a r ( A F P ) a r ( P C B ) = ( F P C B ) 2 = 4 49 . . . . . . . ( 3 ) a r ( D P E ) a r ( P C B ) = ( P E C B ) 2 = 9 49 . . . . . . . . ( 4 ) F P P E = 2 3 . . . . . . . . ( 5 ) U s i n g ( 1 ) , ( 2 ) , ( 3 ) , ( 4 ) a n d ( 5 ) w e g e t L K = 6 ( F P ) S i n c e , A F P J L K a r ( J L K ) a r ( A F P ) = ( L K F P ) 2 = 36 T h e r e f o r e , a r ( J L K ) = 36 × 4 = 144 FPCL\quad and\quad EPBK\quad are\quad parallelograms\\ \Longrightarrow FP=LC.......(1)\\ \quad \quad \quad \quad PE=BK.......(2)\\ \triangle AFP\sim \triangle PCB\\ \triangle DPE\sim \triangle PCB\\ \\ therefore,\quad \frac { ar(\triangle AFP) }{ ar(\triangle PCB) } ={ (\frac { FP }{ CB } })^{ 2 }=\frac { 4 }{ 49 } .......(3)\\ \quad \quad \quad \quad \quad \quad \quad \quad \quad \frac { ar(\triangle DPE) }{ ar(\triangle PCB) } ={ (\frac { PE }{ CB } })^{ 2 }=\frac { 9 }{ 49 } ........(4)\\ \Longrightarrow \frac { FP }{ PE } =\frac { 2 }{ 3 } ........(5)\\ Using\quad (1),(2),(3),(4)\quad and\quad (5)\quad we\quad get\quad \\ LK=6(FP)\quad \\ Since,\quad \triangle AFP\sim \triangle JLK\quad \quad \quad \quad \quad \\ \quad \quad \frac { ar(\triangle JLK) }{ ar(\triangle AFP) } ={ (\frac { LK }{ FP } })^{ 2 }=36\\ Therefore,\quad ar(\triangle JLK)=\quad 36\quad \times \quad 4\quad =\boxed{144}

@Abhijeet Verma You are awesome in geometry.. which city do you belong to? Are you in std11?

Pulkit Deshmukh - 5 years, 9 months ago

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Well, if you can't see my city, here's some help for you- I live in a city which was developed by Dost Mohammed (1708-1740) (one of Emperor Aurangazeb's Afghan governors), with a current (not really current) population of 2,368,145, spawning over an area of 2,772 sq km, with STD code 0755 and with a literacy rate of 82.3%.

So, can you guess? {btw, I am in class 9(lol)}

Abhijeet Verma - 5 years, 9 months ago

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@Abhijeet Verma Sir , u are awesome .... failing 2 years and still ...

Ayush Choubey - 5 years, 9 months ago

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@Ayush Choubey @Ayush Choubey Yeah, but you defeated me there as well! damn it! I came to know you failed four times!

Abhijeet Verma - 5 years, 9 months ago

So you live in Bhopal;which school do you attend,and which coaching ,as a lot of people go to coaching from 9th itself in the city

Pulkit Deshmukh - 5 years, 9 months ago

@Pulkit Deshmukh Great problem. @Abhijeet Verma Even better solution.

I made a damn silly error. Curse me.

Mehul Arora - 5 years, 9 months ago

Triangles where the areas are given are all similar. . . . . N o t e ; 49 4 = 7 2 . . . . . . . 9 4 = 3 2 . ....Note; \sqrt{\dfrac{49}{4}} =\dfrac 7 2. ......\sqrt{\dfrac{9}{4} }=\dfrac 3 2.
WLOG AP=2x, FP=4.......Then because of similarity, P B = 7 2 2 x = 7 x , C B = 7 2 4 = 14 , . . . . . . D E = 3 2 2 x = 3 x , P E = 3 2 4 = 6. PB=\dfrac 7 2 *2x=7x, CB=\dfrac 7 2 *4=14,......DE=\dfrac 3 2 * 2x=3x, PE=\dfrac 3 2 * 4=6.
FLCP, JAPD, and EPBK are | |grams. Implies LC=FP=4, .. BK=PE=6, ..JD=AP=2x, ..EK=PB=7x.
So LK=LC+CB+BK=24. ...... JK=JD+DE+EK=12x.
Triangle PCB=1/2 * PB * CB=49x=49 square units. So x=1.
So area JLK=1/2 * LK * JK=1/2 * 24 * 12 * 1= 144. \color{#D61F06}{144}.



Pulkit Deshmukh
Sep 5, 2015

@Abhijeet Verma thanx for posting a solution

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