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If ∣a⃗∣=∣b⃗∣=∣a⃗+b⃗∣=1\lvert\vec{a}\rvert = \lvert\vec{b}\rvert = \lvert\vec{a}+\vec{b}\rvert = 1, then

Match List-I with List-II

LIST-ILIST-II
A. ∣a⃗−b⃗∣\lvert\vec{a}-\vec{b}\rvertI. 2π3\dfrac{2\pi}{3}
B. Angle between a⃗\vec{a} and b⃗\vec{b}II. −12-\dfrac{1}{2}
C. Angle between a⃗\vec{a} and a⃗+b⃗\vec{a}+\vec{b}III. 3\sqrt3
D. a⃗.b⃗\vec{a}.\vec{b}IV. π3\dfrac{\pi}{3}

Choose the correct answer from the options given below:

Solution

✅ Correct Option: 1

From 1=1+1+2a⃗⋅b⃗1=1+1+2\vec a\cdot\vec b, a⃗⋅b⃗=−12\vec a\cdot\vec b=-\dfrac12 (D-II), so the angle is 2π3\dfrac{2\pi}{3} (B-I).

∣a⃗−b⃗∣2=1+1+1=3|\vec a-\vec b|^2=1+1+1=3, giving 3\sqrt3 (A-III).

a⃗⋅(a⃗+b⃗)=12\vec a\cdot(\vec a+\vec b)=\dfrac12 with both magnitudes 1, so that angle is π3\dfrac{\pi}{3} (C-IV).

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