Throughout this course (and in many areas of mathematical physics) it is extremely convenient to write one function of interest as a weighted superposition of another set of functions whose behavior we are familiar with. If our system is linear, we can then analyze the behavior of the system on our function of interest by breaking it up into its components parts and adding up the results. This is the basis of functional analysis which is closely related to linear algebra. For that reason, many geometrical concepts can be leveraged in functional analysis to help understand what’s going on.