In the section on uniform circular motion, the book uses the equation (Δv / v) = (Δr / r) to represent the relationship between the change in velocity and the change in radius. Then, they substitute Δv into the formula for average acceleration, which is Average acceleration = Δv / Δt. My first question is why can they use this equation to substitute into the Δv in the average acceleration equation, which represents the difference between two vectors? The book mentions that the relationship from the similar triangles is about their length, so the magnitude of the vectors. Upon further inspection, I noticed that the 'a' in the equation is not bold, indicating magnitude. Why can they use the same equation and just change it to equal the magnitude? Is it something about the assumptions taken for uniform circular motion that allows for these calculations?