Triple Integral

TRIPLE INTEGRALS Just as we defined -single integrals for functions of one variable -double integrals for functions of two variables, so we can define triple integrals for functions of three variables.

Consider f (x,y,z) defined on a rectangular box:

The first step is to divide B into sub-boxes—by dividing: – The interval [a, b] into l subintervals [x i-1, x i ] of equal width Δx. – [c, d] into m subintervals of width Δy. – [r, s] into n subintervals of width Δz.

The planes through the endpoints of these subintervals parallel to the coordinate planes divide the box B into lmn sub-boxes -Each sub-box has volume ΔV = Δx Δy Δz

Then, we form the triple Riemann sum where the sample point is in B ijk.

The triple integral of f over the box B is: if this limit exists. – Again, the triple integral always exists if f is continuous. TRIPLE INTEGRAL

We can choose the sample point to be any point in the sub-box. However, if we choose it to be the point (x i, y j, z k ) we get a simpler-looking expression:

FUBINI’S Theorem (TRIPLE INTEGRALS ) If f is continuous on the rectangular box B = [a, b] x [c, d] x [r, s], then

The iterated integral on the right side of Fubini’s Theorem means that we integrate in the following order: 1.With respect to x (keeping y and z fixed) 2.With respect to y (keeping z fixed) 3.With respect to z

Evaluate the triple integral where B is the rectangular box Example 1

Example-2

Volume

Example-3

Example-4

Class work