|a| = |b| = 1, |c| = 2 and a x (a x c) + b = 0: acute angle between a and c

1. A.
   $\frac{\pi}{6}$
2. B.
   $\frac{\pi}{4}$
3. C.
   $\frac{\pi}{3}$
4. D.
   $\frac{\pi}{2}$

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1. A.
   $\frac{\pi}{3}$
2. B.
   $\frac{\pi}{6}$
3. C.
   $\frac{\pi}{4}$
4. D.
   $\frac{\pi}{12}$

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1. A.
   1
2. B.
   $\dfrac{3}{2}$
3. C.
   $\dfrac{4}{3}$
4. D.
   $\dfrac{2}{\sqrt{3}}$

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1. A.
   $\dfrac{\pi}{4}$
2. B.
   $\dfrac{\pi}{6}$
3. C.
   $\dfrac{\pi}{3}$
4. D.
   $\dfrac{\pi}{8}$

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1. A.
   $\dfrac{\pi}{2}$
2. B.
   $\dfrac{\pi}{3}$
3. C.
   $\dfrac{\pi}{4}$
4. D.
   $\dfrac{\pi}{6}$

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