>>180
敿宎10񎵳偺墌偺拞怱傪O偲偟偰佢AOB=兤偲偡傞丅
嶰墌偑屳偄偵愙偡傞帪OA=6B=5B=9傛傝cos兤=-1/3
1亞cos兤亞-1/3偱擇墌偼廳側傞偺偱y=cos兤偲0亝兤亝兛:(cos兛=-1/3)偱埻傑傟傞柺愊偲0亝兤亝兾偱埻傑傟傞柺愊偺斾棪傪弌偡