Math Triple Integrals in Cylindrical Coordinates

Transcription

1 Math Triple Integrals in Cylindrical Coordinates Peter A. Perry University of Kentucky November 2, 218

2 Homework Re-read section 15.7 Work on section 15.7, problems 1-13 (odd), (odd) from Stewart Read section 15.8 for Monday November 5 Begin webwork C3

3 Unit III: Multiple Integrals Lecture 24 Lecture 25 Lecture 26 Lecture 27 Lecture 28 Lecture 29 Lecture 3 Lecture 31 Lecture 32 Lecture 33 Lecture 34 Double Integrals over Rectangles Double Integrals over General Regions Double Integrals in Polar Coodinates Applications of Double Integrals Surface Area Triple Integrals Triple Integrals in Cylindrical Coordinates Triple Integrals in Spherical Coordinates Change of Variable in Multiple Integrals, Part I Change of Variable in Multiple Integrals, Part II Exam III Review

4 Goals of the Day Understanding Applications of Triple Integrals Know how to locate points and describe regions in cylindrical coordinates Know how to evaluate triple integrals in cylindrical coordinates

5 Volume Recall that the area of a region D in the xy plane is given by the double integral A(D) = 1 da 2 2 Similarly, the volume of a region E is the triple integral V (E ) = 1 dv E Find the volume of the solid enclosed by the paraboloids y = x 2 + z 2 and y = 8 x 2 z 2

6 Cylindrical Coordinates z Add the z-coordinate to polar coordinates and you get cylindrical coordinates θ r y x

7 Cylindrical Coordinates Add the z-coordinate to polar coordinates and you get cylindrical coordinates z (r, θ, z) z θ r y x

8 Cylindrical Coordinates Add the z-coordinate to polar coordinates and you get cylindrical coordinates r = x 2 + y 2, x = r cos θ, tan θ = y/x y = r sin θ r y θ x

9 Cylindrical Coordinates Add the z-coordinate to polar coordinates and you get cylindrical coordinates r = x 2 + y 2, x = r cos θ, tan θ = y/x y = r sin θ r y θ x 1. Find the cylindrical coordinates of the point ( 1, 1, 1) 2. Find the cyindrical coordinates of the point ( 2, 2 3, 3) 3. Find the rectangular coordinates of the point (4, π/3, 2)

10 Equations and Regions in Cylindrical Coordinates z 1. Identify the surface r = 2 sin θ y x

11 Equations and Regions in Cylindrical Coordinates 1. Identify the surface r = 2 sin θ 2. Write the equation 5 2x 2 + 2y 2 z 2 = in cylindrical coordinates 5 5 5

12 Equations and Regions in Cylindrical Coordinates 1. Identify the surface r = 2 sin θ 2. Write the equation 2x 2 + 2y 2 z 2 = 4 in cylindrical coordinates 3. Sketch the solid described by the inequalities θ π/2, r z 2

13 Equations and Regions in Cylindrical Coordinates 1. Identify the surface r = 2 sin θ 2 2. Write the equation 2x 2 + 2y 2 z 2 = in cylindrical coordinates 3. Sketch the solid described by the inequalities θ π/2, r z 2

14 Triple Integrals in Cylindrical Coordinates In polar coordinates da = r dr dθ So, in cylindrical coordinates, If E is the region dv = r dr dθ dz = r dz dr dθ E = {(x, y, z) : (x, y) D, u 1 (x, y) z u 2 (x, y)} then E f (x, y, z) dv = D ( u2 (x,y) u 1 (x,y) ) f (x, y, z) dz da If we can describe D in polar coordinates: then we can evaluate f (x, y, z) dv = E D = {(r, θ) : α θ β, h 1 (θ) r h 2 (θ)} β h2 (θ) u2 (r cos θ,r sin θ) f (r cos θ, r sin θ, z) r dz dr dθ α h 1 (θ) u 1 (r cos θ,r sin θ)

15 Step by Step β h2 (θ) u2 (r cos θ,r sin θ) f (x, y, z) dv = f (r cos θ, r sin θ, z) r dz dr dθ E α h 1 (θ) u 1 (r cos θ,r sin θ) This formula summarizes a multi-step process. If then, to use the formula: E = {(x, y, z) : (x, y) D, u 1 (x, y) z u 2 (x, y)} 1. Substitute x = r cos θ, y = r sin θ into u 1 and u 2 to find the limits of the inmost integral 2. Substitute x = r cos θ, y = r sin θ into the formula for f (x, y, z) to rewrite f as a function of r, θ, and z 3. After making these substitutions, evaluate the triple iterated integral

16 Triple Integrals in Cylindrical Coordinates β h2 (θ) u2 (r cos θ,r sin θ) f (x, y, z) dv = f (r cos θ, r sin θ, z) r dz dr dθ E α h 1 (θ) u 1 (r cos θ,r sin θ) 1. Find E z dv where E is enclosed by the paraboloid 4 2 z = x 2 + y 2 and the plane z =

17 Triple Integrals in Cylindrical Coordinates β h2 (θ) u2 (r cos θ,r sin θ) f (x, y, z) dv = f (r cos θ, r sin θ, z) r dz dr dθ E α h 1 (θ) u 1 (r cos θ,r sin θ) 1. Find E z dv where E is enclosed by the paraboloid 1 5 z = x 2 + y 2 and the plane z = Find E (x y) dv if E is the solid which lies between the cylinders x 2 + y 2 = 1, x 2 + y 2 = 16, above the xy plane, and below the plane z = y + 4.