If the magnitude of sum of two vectors is equal to the magnitude of difference of the two vectors, the angle between these vectors is

A particle moves so that its position vector is given by $$\overrightarrow r = \cos \omega t\,\widehat x + \sin \,\omega t\,\widehat y,$$ where $$\omega $$ is a constant.

Which of the following is true?

If vectors $$\overrightarrow A = \cos \omega t\widehat i + \sin \omega t\widehat j$$ and $$\overrightarrow B = \cos {{\omega t} \over 2}\widehat i + \sin {{\omega t} \over 2}\widehat j$$ are functions of time, then the value of t at which they are orthogonal to each other is

The positions vector of a particle $$\overrightarrow R $$ as a function of time is given by $$\overrightarrow R $$ = 4sin(2$$\pi $$t)$$\widehat i$$ + 4cos(2$$\pi $$t)$$\widehat j$$. Where R is in meters, t is in seconds and $$\widehat i$$ and $$\widehat j$$ denote unit vectors along x-and y-directions, respectively. Which one of the following statements is wrong for the motion of particle?