解:∵三角形A1B1C1∽三角形ABC∴AB:A1B1=BC:B1C1=AC:A1C1A1B1+B1C1+A1C1=81解得A1B1=18,B1C1=27,A1C1=36
81:(12+18+24)=81:54=3:2也就是三角形A1B1C1与ABC边长之比是3:2A1B1=12×3/2=18cmB1C1=18×3/2=27cmA1C1=24×3/2=36cm