Linear approximation is a method of approximating otherwise difficult to find values of a mathematical function by taking the value on a nearby tangent line instead of the function itself. This process is also called tangent line approximation.

In some situations, it is easy to calculate the value f(a) of a function f, but difficult or impossible to calculate nearby values of f. In this case, mathematicians calculate the tangent line of the graph of f at the point (a, f(a)) and use values calculated by this line instead of f itself.