What is meant by if the axis of rotation is fixed (the direction of angular v and angular a is fixed) the vector equation reduces to scalar eq? Angular a =d angular v/dt

dear student

The relation between angular velocity and angular acceleration is given by
$\overrightarrow{\alpha }=\frac{d\overrightarrow{\omega }}{dt}$
The above equation is a vector differential equation and the directions of the angular acceleration and angular velocity can be change during the motion as in the case of precession motion of a top so we have to use the vector equation for the study of motion. But if we fixed the axis of rotation then the motion will be in a plane and the direction also fixed so we can take only magnitude of vector quantities in the equation. Thus vector equation reduces to a scalar equation.