Question

Let two non-collinear unit vectors a and b form an acute angle. A point P moves so that at any time t, the position vector OP(where O is the origin) is given by a cos t + b sin t, where P is the farthest from origin O, let M be the length of OP and u be the unit vector along OP. Then

Answer 1

Answer is (a) 

Explanation:

Given

OP = a cos t + b sin t

|OP|² = |a cos t|² = |b sin t|² + 2(a.b)sin t cos t