👉 The term "curvilinear" refers to a curve that is not straight, but instead has an angle or curvature. It's similar to how curves in space can be curved on their own without being straight. For example, consider the curve y = x^3 + 2x^2 + 1. This curve has an angle of π/6 radians (or approximately 45 degrees) at its vertex, which is not straight but rather curvilinear due to the presence of