I've got a problem where I need to numerically integrate a multivariable function but I'm not sure how to do this. I'm more than familiar with how to numerically integrate a single variable function numerically but I have no clue how to do this for a multivariable function. For example lets say I have the function P = (x2 + 4xy) and I need to integrate this numerically between some definite closed bounds of x, y, and z using the trapezoidal rule. How would one go about doing this? Would I simply perform the integration on each variable and then plug that solution into the respective variable for that function for each integral I evaluate? I have two books on numerical methods and none of them mention anything about doing this. Is it even possible?