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Question Number 112060 by Aina Samuel Temidayo last updated on 06/Sep/20
In a trapezium, ABCD, with AB  parallel to CD. If M is the midpoint of  line segment AD and P is a point on  line BC such that MP is perpendicular  to BC. Show that, we need only the  lengths of line segments MP and BC  to calculate the area ABCD.
Inatrapezium,ABCD,withABparalleltoCD.IfMisthemidpointoflinesegmentADandPisapointonlineBCsuchthatMPisperpendiculartoBC.Showthat,weneedonlythelengthsoflinesegmentsMPandBCtocalculatetheareaABCD.
Answered by 1549442205PVT last updated on 06/Sep/20
Commented by Aina Samuel Temidayo last updated on 06/Sep/20
Thanks. Please what about the  solution?
Thanks.Pleasewhataboutthesolution?
Commented by 1549442205PVT last updated on 06/Sep/20
Denote by G midpoint of BC   Suppose known MP=m,BC=a,then  S_(BMC) =((BC.MP)/2)=((am)/2).We prove that  S_(ABCD) =2S_(BMC) .Indeed,Denote byI,H  orthogonal projections of points B and  C on MG respectively.Then S_(CMG) =  ((MG.CH)/2),S_(BMG) =((MG.BI)/2)  S_(BMC) =S_(CMG) +S_(BMG) =((MG(BI+CH))/2)(1)  Since M,G are midpoints of BC and  AD ,MG is midline of the trapezium  ABCD.Since AB//CD,BI+CH equal  to altitude h of the trapezium .  Therefore,MG=((AB+CD)/2),BI+CH=h  and S_(ABCD) =(((AB+CD).h)/2)=MG.h(2)  From (1) and (2) we infer  S_(ABCD) =2S_(BMC) =a.m .That thing show  that only need know the length of the  line segments BC and MP we can  calculate the area of the trapezium
DenotebyGmidpointofBCSupposeknownMP=m,BC=a,thenSBMC=BC.MP2=am2.WeprovethatSABCD=2SBMC.Indeed,DenotebyI,HorthogonalprojectionsofpointsBandConMGrespectively.ThenSCMG=MG.CH2,SBMG=MG.BI2SBMC=SCMG+SBMG=MG(BI+CH)2(1)SinceM,GaremidpointsofBCandAD,MGismidlineofthetrapeziumABCD.SinceAB//CD,BI+CHequaltoaltitudehofthetrapezium.Therefore,MG=AB+CD2,BI+CH=handSABCD=(AB+CD).h2=MG.h(2)From(1)and(2)weinferSABCD=2SBMC=a.m.ThatthingshowthatonlyneedknowthelengthofthelinesegmentsBCandMPwecancalculatetheareaofthetrapezium
Commented by Aina Samuel Temidayo last updated on 06/Sep/20
Please check my other questions out. I  need help please.
Pleasecheckmyotherquestionsout.Ineedhelpplease.
Commented by Aina Samuel Temidayo last updated on 06/Sep/20
Please how did you know  S_(ABCD ) =2S_(BMC) ?
PleasehowdidyouknowSABCD=2SBMC?
Commented by 1549442205PVT last updated on 06/Sep/20
I proved above!It follows from(1)&(2)
Iprovedabove!Itfollowsfrom(1)&(2)
Commented by Aina Samuel Temidayo last updated on 06/Sep/20
Ok. Thanks. Please check the  question I just posted.
Ok.Thanks.PleasecheckthequestionIjustposted.

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