Topic Covered: Evaluation of Double Integrals by changing the order of Integration. The multiple integral is a definite integral of a function of more than one real variable, for instance, f(x, y) or f(x, y, z). Integrals of a function of two variables over a region in R^2 are called double integrals, and integrals of a function of three variables over a region of R^3 are called triple integrals. Double integrals are used to calculate the area of a region, the volume under a surface, and the average value of a function of two variables over a rectangular region. Do Like & Share these videos with your friends. If you are watching for the first time then Subscribe to my Channel and press the bell icon to stay updated for more videos around Engineering Mathematics. Prof. Sunil Department of Mathematics & Scientific Computing, NIT Hamirpur (HP)