Question

已知线段AB上有C、D两点,AC=1/3BC,AD=4/5BD,CD=21/4cm,求线段AB的长.

Answer 1

因为,AC/BC = 1/3 ,AD/BD = 4/5 ,所以,AC/AB = AC/(AC+BC) = 1/(1+3) = 1/4 ,AD/AB = AD/(AD+BD) = 4/(4+5) = 4/9 ,可得：AC = (1/4)AB ,AD = (4/9)AB ；因为,CD = AD-AC = (7/36)AB ,所以,AB = (36/7)CD = 27 cm ....