The document discusses odd and even functions. It defines odd functions as those where f(-x) = -f(x), and provides examples such as y = x and y = x^3 + x^7. It proves that y = x^3 + x^7 is an odd function. Even functions are defined as those where f(-x) = f(x), with examples like y = x^2 + 4. It proves y = x^2 + 4 is an even function by showing f(-x) = f(x).