A = 339.531 units^2 Â
Step-by-step explanation:
Given:-
- The surface of consideration is bounded by the following:
          Cylinder : Â
          Planes : x = 3 , y = 18
Find:-
Find the area of the surface in the first octant
Solution:-
- It is better to sketch the given curves. Taking (y-z) plane on the sketch paper with x - axis out of the page.
- We see that a surface bounded with 5 faces. We will investigate each face one by one.
Face 1 : This face that lies on the y-z plane defined by the curve of the cylinder and y = 18, and z = x = 0.
  The Area of this face can be calculated by using integral calculus.
                    Â
  The limits a,b corresponds to a = y = 18 and b = 0. Evaluate Integral.
                 Â
Face 2: This face has the same area as Face 1. This lies on the plane x = 3 defined by the curve and y = 18, z = 0.
                  A1 = A2 = 97.19994 units^2
Face 3 : This face lies on the plane where y = 18 parallel to x-z plane. Representing a rectangle, defined by plane y = 18 where it intersects the cylinder and z = 0 ... Denoting width of rectangle. While the length is defined by the intersection of planes (y = 18 and x = 3).
The intersection point of y = 18 and cylinder can be determined by equating both equations and compute the value of z coordinate. Â Â Â Â Â
                 Â
The area of the Face 3 can then be calculated from the formula:
                  A3 = Length*Width
                  A3 = (3)*(9)
                  A3 = 27 units^2
Face 4 : This face lies on the plane where z = 0 parallel i.e x-y plane. Representing a rectangle, defined by plane y = 18 where it intersects the z = 0 denoting length, while the width is defined by the intersection of planes (x = 3 and z = 0).
    The area of Face 4 can be calculated directly from rectangle formula:
                 A4 = Length*Width
                 A4 = (3)*(18)
                 A4 = 54 units^2
Face 5 : This face is curved in nature defined by the cylinder. Which starts from plane x = 0 and limits at x = 3. We will determine the Area of this face by first computing the arc length (L) of the cylinder curve defined by:
                Â
The arc length formula (L) is given to be:
               Â
We will use the arc length and integrate with respect to x. From x = 0 to x = 3. We have:
              A5 = L*( 3 - 0 )
              A5 = (21.37736)*(3)
              A5 = 64.13208 units^2
- The total surface area of the enclosed body is:
              A = A1 + A2 + A3 + A4 + A5
              A = 2*(97.1994) + 27 + 54 +64.13208
              A = 339.531 units^2         Â