**TI82** TxtView file generated by CalcText - KouriÐ ÁPSDFBÁ¿ÿsuiteDEFINITION 2: -> -> -> -> u = AB et v = AC -> -> (AB,AC) = alp(2pi) Dans le triangle ACH, rectangle en H AH=Ac.Cos alp -> -> p = AB.AC - - = AB.AH = AB.AC.Cos alp -> -> = ||AB||.||AC||Cos alp *alp apartien [0,pi/2] cos alp>0 p>0 *alp=pi/2 alors p=0 *alp apartien ]pi/2,pi] cos alp<0 et p<0 PROPRIETEES: -> -> u = AB -> -> v = AC -> w = vecteur qcq -> -> -> -> *u.v = v.u (commutatif) -> -> ->-> *kER* (ku).v = k.(u,v) -> ->-> ->->->-> *u.(v+w)=u.v+u.w -> -> -> -> -> -> *(u+v)²= (u+v).(u+v) -> -> -> -> = u² + 2u.v + v² -> -> ->-> donc u.v= 1/2[||u+v||² -> -> -||u||² - ||v||²]ÿǬ