calculus
posted by Anonymous .
Triangle ABC is an equalateral triangle, with O it's centroid.
a) Show that vector OA + vector OB + vector OC = vector 0

OA=OB=OC symmetry
Add components in direction of OA
OA  OB sin 30  OC sin 30
but sin 30=1/2
Add components perpendicular to OA
OCcos 30  OB cos 30 = 0