Let $\hat{a}$ and $\hat{b}$ be two unit vectors. If the vectors $\bar{c}=\hat{a}+2 \hat{b}$ and $\bar{d}=5 \hat{a}-4 \hat{b}$ are perpendicular to each other,then the angle between $\hat{a}$ and $\hat{b}$ is

  • A
    $\frac{\pi}{6}$
  • B
    $\cos^{-1}\left(\frac{1}{3}\right)$
  • C
    $\frac{\pi}{3}$
  • D
    $\cos^{-1}\left(\frac{1}{4}\right)$

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