Which method is used to find the gradient or rate of change of a function?

The method used to find the gradient or rate of change of a function is differentiation. Differentiation involves determining how a function changes as its input changes, effectively calculating the slope of the tangent line to the function at any given point. This slope represents the rate of change of the function with respect to its variable. In practical terms, differentiation allows us to understand how a function behaves and can be applied in various fields such as physics, engineering, and economics to model and analyze dynamic systems.

The other options represent different mathematical concepts. Integration involves finding the accumulated area under a curve and is the reverse operation of differentiation; it does not provide the rate of change directly. Summation refers to adding a series of values together and does not pertain to rates of change. Regression is a statistical method used for modeling relationships between variables, often to predict outcomes, but it does not directly calculate the gradient of a function in the same sense as differentiation does.