设底边YCM,腰XCM
当12cm部分包含底边
X+1/2x=7
1/2x+y=12
2x>y
不构成三角形,舍去
当7CM部分包含底边时
x+1/2x=12
1/2x+y=7
2x>y
x=8
y=3中线呢？？？？这个长度·······不是把周长分成两个部分么？中线长应该不用算进去中线长(根号82)/2无语·····················································································································看看你的答案，任意俩边之和大于第三遍，3+3＞8，，，牛！！！我才真的无语，底边3，腰长8啊，底边只有1条啊，大哥（大姐？）……中线呢？？？？这个长度·······中线呢？？？？这个长度·······