Let â and b̂ be two unit vectors. If the vectors c = a + 2 b and d = 5 a - 4 b are perpendicular to each...

Question

Let â and b̂ be two unit vectors. If the vectors c = a + 2 b and d = 5 a - 4 b are perpendicular to each other, then the angle between â and b̂ is

Accepted Answer

(3)

JEE Main 2012 Mathematics question