Wikipedia:Reference desk/Archives/Mathematics/2007 February 24

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February 24

Length of Curved part of a circle

The answer I get is different to that provided in SMQ8 (Secondary Maths for Queensland) Year 8. Would you please show me where I am wrong. I have been able to work out all the others in Chap 6.5. The question and my workings follow.

Calculate the length of the curved part... In the circle there are two curved areas, opposite each other, both have an angle of 45 degrees. Therefore the curved area is two times 45 degrees of the 360 circumference. Eg 90 degrees of 360 degrees that is one quarter. Next, an arrow showing radius of 15 cm. Circumference = 2radius x pie that is 2x3.14x15 = 94.2 Curved part = 94.2 x .25

My answer 23.5. Answer in book 84 cm I would appreciate your help MathsDaphne Williams 01:40, 24 February 2007 (UTC)

My guess is that they want you to include the line segments connecting the arcs, whose combined lengths amount to four times the radius. Using R for the radius, that results in a total length of (π/2+4)R, or in a round figure 84 cm if R = 15 cm.  --Lambiam^Talk 02:47, 24 February 2007 (UTC)

If the instructions really say "the length of the curved part", then they were wrong to include straight lines in the calcs, so you should be able to argue to have your answer marked as correct. StuRat 00:13, 27 February 2007 (UTC)

Software for category theory diagrams

Hey

I want to create a wikipedia article, but I might need to draw some diagrams. What do people use to make stuff like pullback diagrams?

TIA Bgst 15:11, 24 February 2007 (UTC)

Use a (La)TeX macro package like those by François Borceux or Paul Taylor to create the diagram, and convert it (preferably) to SVG format. Apart from the last conversion step, that is how the diagram at Pushout (category theory) appears to have been created. If you get stuck, possibly its creator User:Fropuff can be of assistance.  --Lambiam^Talk 17:42, 24 February 2007 (UTC)

Fropuff has previous offered to help create diagrams. Also, in November 2006 I answered a similar question at Wikipedia talk:WikiProject Mathematics by pointing at Image:Snake lemma nat.png, the page of which documents its genesis. Most diagrams are simpler, and can use the method of Image:CategoricalPushout-02.png. --KSmrq^T 01:10, 26 February 2007 (UTC)

If you like generalized abstract nonsense, there are programs to create fake Mondrian paintings.172.146.58.73 09:10, 26 February 2007 (UTC)