Functions are similar to equations in that they can be solved for one variable or multiple variables and can be linear or quadratic in form. Functions are different from equations in that each value for x can have only one corresponding y value.
Some rules to remember for functions
 f(x) = g(x) = (f + g)(x)
 f(x) – g(x) = (f  g)(x)
 f(x) * g(x) = (fg)(x)
 f(x) / g(x) = (f/g)(x)
 Composite functions are written (f o g)(x) or f(g(x)) in this case the entire function can replace the x value in the other function.
