# Surface area of circle extracted from a tube wall

I have made a hollow tube (thickness $1$mm) having inner radius $89$ mm and outer radius $90$ mm (length $400$ mm, can be higher). then I made a circular (circle radius $25$ mm) cut perpendicular to tube Length. Now I want to calculate area (from extracted circle of $25$ mm radius) for a radius of $13$ mm from center. Just think in steps: 1. cut a tube from diameter. 2. take any one part of tube 3. now apply above given dimensions 4. you will get a curved Circle.

How Can I calculate radius?

How the area will be calculated as it will be half symmetry. ( I have image but it is saying i need at least 10 reputation to upload image.. i can send if some body need via email.

• I'm missing something. How is the thickness $1$ mm if the inner and outer radii differ by $10$ mm? It would be useful if you added a diagram... – Brian Tung Aug 25 '15 at 16:14
• I have just noticed and edited.. Its 89mm and 90mm,,,.. thnx – Hafiz M Sajjad Aug 25 '15 at 16:14
• You want intersection area between tube radii (90,25 mm) like what is centrally removed by drilling out, right? But I do not understand 13 mm. Can you sketch? – Narasimham Aug 25 '15 at 16:21
• I can send Image via Email.. it is saying i need at least 10 reputation for image uploade :( – Hafiz M Sajjad Aug 25 '15 at 16:36
• Is it so that two chord areas are excluded in the smaller circle? – Narasimham Aug 25 '15 at 16:58

I have found the surface area (approx. $1065$ mm^2)with the help of SolidWorks but I want to know Formula to calculate analytically.