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Kaya Renger Coordinator

29/09/2017 at 20:47
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Given right isosceles triangle ABC at A. On AB,AC take D,E so that AD = AE. Line through D \(\perp BE\) and cut BC at I , Line through A \(\perp BE\) cut BC at K. Call M is the intersection of AK and CD.

a) Show that : \(\Delta ABE=\Delta ACD\)

b) \(\Delta MAC\) isosceles

c) M is the midpoint of CD , K is the midpoint of  IC

d) Call G is the intersection of DK and IM , MK cut GC at F.

Show that : FM = FK




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    Phan Thanh Tinh Coordinator 29/09/2017 at 23:23

    B D A E C M K I G N F 1 1 2 1 1

    a) \(\Delta ABE\) and \(\Delta ACD\) have the common angle A ; AB = AC ; AE = AD, so \(\Delta ABE=\Delta ACD\left(S-A-S\right)\)

    b) From a), we have : \(\widehat{B_1}=\widehat{C_1}\). Moreover, \(\widehat{B_1}=\widehat{A_1}\)(since they're both complementary to \(\widehat{A_2}\)). So, \(\widehat{C_1}=\widehat{A_1}\). Hence, \(\Delta MAC\) isosceles at M

    c) From b), we have MA = MC (1)

    Since \(\widehat{C_1}+\widehat{D_1}=90^0;\widehat{A_1}+\widehat{A_2}=90^0;\widehat{C_1}=\widehat{A_1}\), \(\widehat{D_1}=\widehat{A_2}\). Hence, \(\Delta MAD\) isosceles at M. Then, MA = MD (2)

    (1),(2) => MC = MD => M is the midpoint of CD

    \(DI\perp BE;AK\perp BE\Rightarrow\)DI // AK

    \(\Delta DCI\) has MC = MD ; MK // DI, so K is the midpoint of IC

    d) The medians DK, IM of \(\Delta DCI\) intersect at G, so G is the centroid of \(\Delta DCI\). CG cuts DI at N, then ND = NI (3)

    \(\Delta DNC\) has MC = MD ; MF // DN, so F is the midpoint of NC

    => MF is the midsegment of \(\Delta DNC\Rightarrow MF=\dfrac{DN}{2}\) (4)

    Similarly, we have : \(FK=\dfrac{NI}{2}\left(5\right)\)

    (3),(4),(5) => FM = FK

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    Ngô Tấn Đạt 29/09/2017 at 21:00

    I can't draw this triangle.


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