The big idea of differential calculus is the concept of the derivative, which essentially gives us the direction, or rate of change, of a function at any of its points. Learn all about derivatives and how to find them here.
One way of thinking about the derivative is as instantaneous rate of change. This is quite incredible because rate of change is usually found over a period of time, and not at an instant. Get comfortable with this approach here.
There are two ways to define the derivative of function f at point x=a. The formal definition is the limit of [f(a+h)-f(x)]/h as h approaches 0, and the alternative definition is the limit of [f(x)-f(a)]/(x-a) as x approaches a. Make introduction with these two definitions.
The derivative of a function isn't necessarily defined at every point. Learn about the conditions for the derivative to exist, and specifically about how continuity fits with this story (spoiler: for a function to be differentiable at a point it must be continuous at that point, but the other way isn't necessary).
This may blow your mind, but the derivative of a function is a function in itself! Get comfortable in thinking about the derivative as a function that is separate from, but tightly related to, its original function.
If you ever tried to find derivatives using their formal definition, you probably know how tedious that may be. Fortunately, we have ways for finding derivatives much quicker, using differentiation rules! Make your first steps in this fascinating world by working with the more basic rules. For example, the derivative of [f(x)+g(x)] is f'(x)+g'(x), and the derivative of k⋅f(x) is k⋅f'(x).
The power rule says that the derivative of xⁿ is n⋅xⁿ⁻¹. It allows us to quickly find the derivative of any polynomial, and it doesn't even stop there! Make introduction with this simple but powerful rule.
The chain rule says that the derivative of the composite function f(g(x)) is f'(g(x))⋅g'(x). This helps us find the derivative of a composite function. It may be slightly hard to grasp, but its importance cannot be overstated!
The quotient rule says that the derivative of the quotient f(x)/g(x) is [f'(x)g(x)-f(x)g'(x)]/g²(x). This helps us find the derivative of a function which is a quotient of two other, more basic, functions.
Some two-variable relationships cannot be turned into a function, like the circle equation x²+y²=4. Implicit differentiation allows us to find the derivative of y with respect to x, even in such equations.
Implicit differentiation provides us with the relationship between the derivatives of inverse functions: if f and g are inverse functions, then f’(x)=1/(g’(f(x)). Get comfortable working with this relationship.
In logarithmic differentiation, we find the derivative of the natural log of a function instead of the derivative of the function itself. It may surprise you, but this can sometimes actually be easier than regular differentiation, if not the only available option. For example, finding the derivative of xˣ.