JEE Advance - Mathematics (2002 - No. 3)
If $${\overrightarrow a }$$ and $${\overrightarrow b }$$ are two unit vectors such that $${\overrightarrow a + 2\overrightarrow b }$$ and $${5\overrightarrow a - 4\overrightarrow b }$$ are perpendicular to each other then the angle between $$\overrightarrow a $$ and $$\overrightarrow b $$ is
$${45^ \circ }$$
$${60^ \circ }$$
$${\cos ^{ - 1}}\left( {{1 \over 3}} \right)$$
$${\cos ^{ - 1}}\left( {{2 \over 7}} \right)$$