ABOB说明书
内心向量公式推导？
内心向量公式推导？
例：在三角形ABC中,若a*OA向量 b*OB向量 c*OC向量0向量,证明：O为三角形ABC内心.
在三角形ABC中,若a*OA向量 b*OB向量 c*OC向量0向量,且a,b,c为三角形三个内角对应三边长,证明：O为三角形ABC内心.
在纸上先把图画出来,然后延长CO交AB于D:以下全部为向量
所以OAOD DA,OBOD DB,依题意得：
aOA bOB cOC0
所以,a(OD DA) b(OD DB) cOC0
又因为,OD与OC共线,DA与DB共线,所以不妨设,ODkOC
原式变为：(k(a b) c)OC (aDA bDB)0
所以,aDA-bDB,所以DA与DB的长度之比为b/a,所以CD为角平分线.同理可证其他的两条也是角平分线.
aboycalledbob是什么意思？
a boy called bob一个叫鲍伯的男孩例句 A boy called Bob, sitting in the window, Kanyi Ben animal encyclopedia book.一个叫鲍伯的男孩，坐在窗前，看一本动物百科书。
my friendBob，英语作文？
amy friend bob is a cute boy. he has big eyes and small nose. he has yellow hair.
Bob is very smart. he always helps me with my maths.
Bob is kind and love animals.
we all like him.
bob的一天英语作文？
Bob is a middle school student. He gets up at 6:30. He eats breakfast at seven. He goes to school at 7:30. School starts at 8:35. He has four lessons in the morning. He has three lessons in the afternoon. He goes home at five.