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If a⃗\vec{a} and b⃗\vec{b} are two unit vectors inclined at an angle θ\theta, then the value of ∣a⃗−b⃗∣|\vec{a}-\vec{b}| is

Solution

✅ Correct Option: 1

∣a⃗−b⃗∣2=∣a⃗∣2+∣b⃗∣2−2a⃗⋅b⃗=1+1−2cos⁡θ=2(1−cos⁡θ)|\vec{a}-\vec{b}|^2=|\vec{a}|^2+|\vec{b}|^2-2\vec{a}\cdot\vec{b}=1+1-2\cos\theta=2(1-\cos\theta).

Using 1−cos⁡θ=2sin⁡2θ21-\cos\theta=2\sin^2\frac{\theta}{2}, this equals 4sin⁡2θ24\sin^2\frac{\theta}{2}, so ∣a⃗−b⃗∣=2sin⁡θ2|\vec{a}-\vec{b}|=2\sin\frac{\theta}{2}.

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