Jawabanmu

2014-06-20T10:01:16+07:00
AB = B - A = (3,-5,-5)  = ΙABΙ= √3²+(-5)²+(-5)²= √59
AC = C -A = (10,3,3) = ΙACΙ = √118

AB.AC = ΙABΙ ΙACΙ cos α
30.-15.-15 = √59 √118 . cosα
0 = √.... cosα
cos α = 0
α=90
1 2 1