Giải thích các bước giải:

a.Xét $\Delta IDN, \Delta IHE$ có:

$ID=IH$

$\widehat{DIN}=\widehat{HIE}$

$IN=IE$

$\to \Delta IDN=\Delta IHE(c.g.c)$

$\to DN=HE,\widehat{IDN}=\widehat{IHE}\to DN//HE$

b.Xét $\Delta KEH,\Delta KDM$ có:

$KE=KD$

$\widehat{HKE}=\widehat{DKM}$

$KH=KM$

$\to \Delta KHE=\Delta KMD(c.g.c)$

$\to DM=HE, \widehat{KDM}=\widehat{KEH}\to DM//HE$

Mà $DN//HE, DN=HE$

$\to DN=DM(=HE)$

c.Xét $\Delta IDE,\Delta IHN$ có:

$ID=IH$

$\widehat{DIE}=\widehat{HIN}$

$IE=IN$

$\to \Delta DIE=\Delta HIN(c.g.c)$

$\to \widehat{IDE}=\widehat{IHN}$

$\to DE//HN$

d.Xét $\Delta KDH,\Delta KEM$ có:

$KD=KE$

$\widehat{DKH}=\widehat{EKM}$

$KH=KM$

$\to \Delta KDH=\Delta KEM(c.g.c)$

$\to \widehat{KDH}=\widehat{KEM}$

$\to DH//ME$