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Question Number 154475 by mr W last updated on 18/Sep/21

Commented by mr W last updated on 18/Sep/21

find the area of the big triangle whose  sides have the distances d_1 ,d_2 ,d_3  to   the sides a,b,c of the small triangle.

findtheareaofthebigtrianglewhosesideshavethedistancesd1,d2,d3tothesidesa,b,cofthesmalltriangle.

Commented by talminator2856791 last updated on 18/Sep/21

 are the lines parallel?

arethelinesparallel?

Commented by mr W last updated on 18/Sep/21

yes, it is said.

yes,itissaid.

Commented by Tawa11 last updated on 21/Sep/21

great sir

greatsir

Answered by mr W last updated on 19/Sep/21

let Δ=area of triangle ABC  Δ=(√(s(s−a)(s−b)(s−c)))  with s=((a+b+c)/2)    say the incenter of triangle ABC is E  and the radius of incircle is r.  r=(Δ/s)=((2Δ)/(a+b+c))    say the distances from E to the sides  of the triangle A′B′C′ are h_1 , h_2 , h_3   respectively, we have  h_1 =r+d_1   h_2 =r+d_2   h_3 =r+d_3

letΔ=areaoftriangleABCΔ=s(sa)(sb)(sc)withs=a+b+c2saytheincenteroftriangleABCisEandtheradiusofincircleisr.r=Δs=2Δa+b+csaythedistancesfromEtothesidesofthetriangleABCareh1,h2,h3respectively,wehaveh1=r+d1h2=r+d2h3=r+d3

Commented by mr W last updated on 19/Sep/21

Commented by mr W last updated on 20/Sep/21

it is obvious that both triangles are  similar, since their sides are parallel  to each other.  say the side lengthes of the big  triangle are a′, b′, c′ with  a′=ka  b′=kb  c′=kc   where k is the magnification factor.    say the area of the big triangle A′B′C′  is Δ′. then we have Δ′=k^2 Δ.    on the other side we have  Δ′=((a′×h_1 )/2)+((b′×h_2 )/2)+((c′×h_3 )/2)  Δ′=((ka×(r+d_1 ))/2)+((kb×(r+d_2 ))/2)+((kc×(r+d_3 ))/2)  Δ′=(k/2)[(a+b+c)r+ad_1 +bd_2 +cd_3 ]  Δ′=(k/2)[(a+b+c)((2Δ)/((a+b+c)))+ad_1 +bd_2 +cd_3 ]  Δ′=(k/2)(2Δ+ad_1 +bd_2 +cd_3 )  since Δ′=k^2 Δ,  (k/2)(2Δ+ad_1 +bd_2 +cd_3 )=k^2 Δ  ⇒k=1+((ad_1 +bd_2 +cd_3 )/(2Δ))  therefore the area of big triangle is  Δ′=(1+((ad_1 +bd_2 +cd_3 )/(2Δ)))^2 Δ

itisobviousthatbothtrianglesaresimilar,sincetheirsidesareparalleltoeachother.saythesidelengthesofthebigtrianglearea,b,cwitha=kab=kbc=kcwherekisthemagnificationfactor.saytheareaofthebigtriangleABCisΔ.thenwehaveΔ=k2Δ.ontheothersidewehaveΔ=a×h12+b×h22+c×h32Δ=ka×(r+d1)2+kb×(r+d2)2+kc×(r+d3)2Δ=k2[(a+b+c)r+ad1+bd2+cd3]Δ=k2[(a+b+c)2Δ(a+b+c)+ad1+bd2+cd3]Δ=k2(2Δ+ad1+bd2+cd3)sinceΔ=k2Δ,k2(2Δ+ad1+bd2+cd3)=k2Δk=1+ad1+bd2+cd32ΔthereforetheareaofbigtriangleisΔ=(1+ad1+bd2+cd32Δ)2Δ

Commented by Rasheed.Sindhi last updated on 20/Sep/21

Wonderful Sir!

WonderfulSir!

Commented by mr W last updated on 20/Sep/21

thanks for reviewing sir!

thanksforreviewingsir!

Answered by Rasheed.Sindhi last updated on 19/Sep/21

Commented by Rasheed.Sindhi last updated on 19/Sep/21

△ABC∼△A′B′C′  △ABC has been moved so that  A coincides A′  ∠BAC  coinsides ∠B′A′C′  d2=d3=0 in this case.  Continue

ABCABCABChasbeenmovedsothatAcoincidesABACcoinsidesBACd2=d3=0inthiscase.Continue

Commented by mr W last updated on 19/Sep/21

((ah_a )/2)=Δ  h_a =((2Δ)/a)  Δ′=(((h_a +d_1 )/h_a ))^2 Δ=(1+(d_1 /((2Δ)/a)))^2 Δ=(1+((ad_1 )/(2Δ)))^2 Δ    using my formula with d_2 =d_3 =0  Δ′=(1+((ad_1 )/(2Δ)))^2 Δ ✓

aha2=Δha=2ΔaΔ=(ha+d1ha)2Δ=(1+d12Δa)2Δ=(1+ad12Δ)2Δusingmyformulawithd2=d3=0Δ=(1+ad12Δ)2Δ

Commented by mr W last updated on 19/Sep/21

i have revised my solution above.  please critical review! thanks!

ihaverevisedmysolutionabove.pleasecriticalreview!thanks!

Commented by Rasheed.Sindhi last updated on 19/Sep/21

Thanks to help for completing my  approach also.

Thankstohelpforcompletingmyapproachalso.

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