If and are perpendicular vectors, + = 13 and =5,find the value of .

If and are two unit vectors such that + is also a unit vector, then find the angle between and
If and are unit vectors, then what is the angle between and , so that - is a unit vector ?
Write the value of λ so that the vectors = and = are perpendicular to each other ?
Find the differential equation representing the family of curves where A and B are arbitrary constants.