. . 513 . ABCa,b,c C 90

A B Ca,b,c. a,b,c

.

,3mAB,AO,AO2.5m,A0.5m,B0.5m?DBDBDBD=ODOBODOB,RtOCDRtAOB.RtAOBOB2= OB= .AB2OA2RtCODOD2= OD= .CD2OC2A0.5mB0.58m.

BC13

.11

02 1 3 54 1

1.258610 ABC101068ED

2.5125 ABCAB.RtABC AB=5BC=12 DAD=AC+CD=13+5=1818.

3.,10mAB,8m.1m,0.1ABC108AB1.1m.

36.52.5?

,12,3,A,AB , ? (3) ?

12cmBA18cm (3) AB2=92+122=81+144=225= AB=15(cm)15.152

1.,,,,,,!?,?3cm,4cm,?

22cm1cm4cmAB,,?AB/43

1. .3. .2. .4. .P51P53