线段的相等与和差倍分

题目

线段的相等与和差倍分
BC=6cm,BD=7cm,点D是AC的中点,求线段AB和AC的长?
要计算过程.
............

答案

①如果是线段BCD,
AB=AD+BD
=CD+BD
=BD-BC+BD
=2BD-BC
=2×7-6
=14-6
=8
AC=2CD
=2(BD-BC)
=2(7-6)
=2
②如果是线段DBC
AB=AD+DB
=CD+DB
=DB+BC+DB
=2DB+BC
=2×7+6
=20
AC=2DC
=2(DB+BC)
=2(7+6)
=26