I have a hard time grasping integration method concepts, My professor asked me (in a PID control class) that how many types of integration are there (as I had done a few approximation in numerical analysis class Riemann sum , simpson approximation , trapezoid) he told me there are 3 methods back euler , forward euler and tustin , but when I checked back euler , forward euler are difference approximation , am I missing something really basic?
also why is trapezoid approximation called billinear transform as billinear transform as far as I know to transform from continuous time domain to discrete tie domain (s<=>Z) and viceversa