解:∵菱形ABCD的周长为8cm,∴菱形的边长为8÷4=2cm,∵∠ABC:∠BAD=2:1,∠ABC+∠BAD=180°(菱形的邻角互补),∴∠BAD=×180°=60°,∴△ABD是等边三角形,∴BD=2cm,∵菱形ABCD对角线AC、BD相交于点O,∴AO=CO,BO=DO=1且AC⊥BD,∴AO===,∴AC=2AO=2.∴BD=2,AC=2.
A.,,B.1,,C.0.3,0.4,0.5D.5,12,13
A.90°B.60°C.45°D.30°
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