Given →a+→b+→c=0 ......(1)
Multiplying →a in both the sides.
→a×(→a+→b+→c)=→a×→0
⇒→a×→a+→a×→b+→a×→c=→0 [∵→a×→a=→0
⇒→a×→b−→c×→a=→0 [∵→a×→c=−→c×→a]
⇒→a×→b=→c×→a .......(2)
Multiplying →b in both the sides of equation (1) we have,
→b×(→a+→b+→c)=→b×→0
⇒→b×→a+→b×→b+→b×→c=→0
⇒→b×→a+→b×→c=→0 [∵→b×→b=→0]
⇒−→a×→b+→b×→c=→0 [∵→b×→a=−→a×→b]
⇒→a×→b=→b×→c .......(3)
By equation (2) and (3) we get,
→a×→b=→b×→c=→c×→a.