In this video, we'll understand 3D rotations from the point of view of vector analysis and quaternions. We will solve the problem of rotating a vector which is perpendicular to the axis of rotation in this video which will help us solve the general case in the next video. We will especially see that the role of the exponential function and Euler's formula in rotations, just as we noticed for the complex numbers, this time with a quaternion power instead of a complex number.