Now, (a+b)×(a×b) ‌⇒a×(a×b)+b×(a×b) ‌=(a⋅b)a−(a⋅a)b+(b⋅b)a−(b⋅a)b ‌‌‌‌‌‌‌[∵a‌ and ‌b‌ are unit vectors ‌∴a⋅a=b⋅b=1] ‌=(a⋅b)a−b+a−(b⋅a)b ‌=(a⋅b)(a−b)+a−b ‌=(a−b)(a⋅b−1) ∴ Given vector is parallel to (a−b).