如图,角 α " role="presentation" style="box-sizing: content-box; -webkit-tap-highlight-color: rgba(0, 0, 0, 0); margin: 0px; padding: 5px 2px; display: inline-block; line-height: 0; overflow-wrap: normal; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; border: 0px; color: rgb(51, 51, 51); font-family: "Microsoft YaHei", arial, SimSun, sans-serif, tahoma; background-color: rgb(255, 255, 255); position: relative;"> α α , β " role="presentation" style="box-sizing: content-box; -webkit-tap-highlight-color: rgba(0, 0, 0, 0); margin: 0px; padding: 5px 2px; display: inline-block; line-height: 0; overflow-wrap: normal; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; border: 0px; color: rgb(51, 51, 51); font-family: "Microsoft YaHei", arial, SimSun, sans-serif, tahoma; background-color: rgb(255, 255, 255); position: relative;"> β β 均以 O x " role="presentation" style="box-sizing: content-box; -webkit-tap-highlight-color: rgba(0, 0, 0, 0); margin: 0px; padding: 5px 2px; display: inline-block; line-height: 0; overflow-wrap: normal; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; border: 0px; color: rgb(51, 51, 51); font-family: "Microsoft YaHei", arial, SimSun, sans-serif, tahoma; background-color: rgb(255, 255, 255); position: relative;"> O x O x 为始边,终边与单位圆 O " role="presentation" style="box-sizing: content-box; -webkit-tap-highlight-color: rgba(0, 0, 0, 0); margin: 0px; padding: 5px 2px; display: inline-block; line-height: 0; overflow-wrap: normal; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; border: 0px; color: rgb(51, 51, 51); font-family: "Microsoft YaHei", arial, SimSun, sans-serif, tahoma; background-color: rgb(255, 255, 255); position: relative;"> O O 分别交于点 A " role="presentation" style="box-sizing: content-box; -webkit-tap-highlight-color: rgba(0, 0, 0, 0); margin: 0px; padding: 5px 2px; display: inline-block; line-height: 0; overflow-wrap: normal; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; border: 0px; color: rgb(51, 51, 51); font-family: "Microsoft YaHei", arial, SimSun, sans-serif, tahoma; background-color: rgb(255, 255, 255); position: relative;"> A A , B " role="presentation" style="box-sizing: content-box; -webkit-tap-highlight-color: rgba(0, 0, 0, 0); margin: 0px; padding: 5px 2px; display: inline-block; line-height: 0; overflow-wrap: normal; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; border: 0px; color: rgb(51, 51, 51); font-family: "Microsoft YaHei", arial, SimSun, sans-serif, tahoma; background-color: rgb(255, 255, 255); position: relative;"> B B ,则 O A → ⋅ O B → = ( ) " role="presentation" style="box-sizing: content-box; -webkit-tap-highlight-color: rgba(0, 0, 0, 0); margin: 0px; padding: 5px 2px; display: inline-block; line-height: 0; overflow-wrap: normal; float: none; direction: ltr; max-width: none; max-height: none; min-width: 0px; min-height: 0px; border: 0px; color: rgb(51, 51, 51); font-family: "Microsoft YaHei", arial, SimSun, sans-serif, tahoma; background-color: rgb(255, 255, 255); position: relative;"> − − → O A ⋅ − − → O B = ( ) O A → ⋅ O B → = ( )