Rajesh Sardar
Last Activity: 10 Years ago
Let [(a+b)×(a×b)] = d.
Now cross product of (a-b) with d will be-
(a-b) × d= (a-b)×[(a+b)×(a×b)]
=(a+b)[(a-b).(a×b)] – (a×b)[(a-b).(a+b)]
= 0 – (a×b)(a2-b2) [ Since a.(a×b) and b.(a×b) both equals to 0
a×(b×c)= b(a.c) – c(a.b) ]
= 0 [Since a and b are unit vector. Hence a2 - b2 =1-1=0]
So we have (a – b) × d = 0 and hence d is parallel to (a – b).
Therofore (a+b)×(a×b) is parallel to (a – b).