This is the definite integral of `F(z) = z^n`. This is referred to as the "power rule," as it works for all functions of single variable with an exponent.1
^ Gradshteyn, I.S. and Ryzhik, I.M. Table of Integrals, Series and Products. Seventh Edition. Academic Press - 2007. ISBN-13: 978-0-12-373637-6, ISBN-10: 0-12-373637-4. eq 2.01-2