The angle between the straight lines, whose direction cosines are given by the equations 2l + 2m $-$ n = 0 and mn + nl + lm = 0, is :

Question

${\pi \over 2}$

$\pi - {\cos ^{ - 1}}\left( {{4 \over 9}} \right)$

${\cos ^{ - 1}}\left( {{8 \over 9}} \right)$

${\pi \over 3}$

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