b) xét tam giác AHB và tam giác DBH ta có:

AH=BD (gt )    BH=BH ( canh chung ) goc AHB= goc HBD (=90)

--> 2 tam giac = nhau theo th (c=g=c)

c) ta co goc ABH= goc BHD ( tam giac AHB= tam giac DBH)

ma goc ABH va goc BHD nam o vi tri so le trong

nen AB//HD

d)xet tam giac BAO va tam giac HDO  ta co

AB=DH ( tam giac ABH= tam giac DBH)

goc OBA= goc OHD (2 goc so le trong va AB//HD)

goc OAB= goc ODH ( 2 goc so le trong va AB//HD)

--> 2 tam giac = nhau ( g=c=g)

--> BO= OH ( 2 canh tuong ung )

--> O la trung diem BH ( O thuoc BH)

d)ta co : goc BDH= goc BAH ( tam giac BDH= tam giac AHB )

ma goc BDH = 35 ( gt)

nen goc BAH=35

ta co:

goc BAH+ goc HAC=90 ( 2 goc ke phu)

goc HAC+goc ACB=90 ( tam giac AHC vuong tai H )

--> goc BAH= goc ACB

--> goc ACB=45