The true statement is:
1
(a̅ × b̅)2 = (a̅)2 (b̅)2 - (a̅ ⋅ b̅)2
2
(a̅ × b̅)2 = (a̅)2 (b̅)2 + (a̅ ⋅ b̅)2
3
If |a̅ + b̅| = |a̅ - b̅| ⇒ a̅ and b̅ are not perpendicular.
4
If a̅ and b̅ are unit vectors and θ is the angle between them, then cos \(\frac{θ}{2} = \frac{1}{2}\)|a̅ - b̅|.