Wikipedia:Reference desk/Archives/Mathematics/2013 December 8

= December 8 =

where can I find a list of mathematics terms?
I have helped to someone that learn with me at the school to learn math, he knows well English more than my language and I would like sometimes to translate the terms to make the math easier for his, but I don't know the English terms, so maybe you would like to give me a list of mathematics terms on English. It will help us to learn together. Thank you! 213.57.115.126 (talk) 21:46, 8 December 2013 (UTC)
 * Term by term you could easily look things up on Wikipedia. If you want lists, we have several at Category:Glossaries of mathematics and Category:Mathematics-related lists. Staecker (talk) 23:37, 8 December 2013 (UTC)

Horizontal transformation factor
This is likely an easy question. I'm a Grade 11 student learning about functions, and this year we learned horizontal transformations (stretch/compression) of various functions (where in grade 10 we were taught only vertical transformations). Now, I had a test on exponential functions, and one of the questions (in the form 2kx) was 20.5x, and I said that it was a horizontal stretch by a factor of 2. My teacher said that it was actually a horizontal stretch by a factor of 0.5, and that the value of the factor was k and not 1/k. Who is right? Thanks. 50.101.203.177 (talk) 22:14, 8 December 2013 (UTC)
 * It could go either way depending on the terminology, but I'd side with you on this one. When you change from 2x to 20.5x the result is to stretch the graph out in the horizontal direction so that features of the graph appear twice as wide as they were before. See these plots. To me it's reasonable to call that a horizontal stretch by a factor of 2. Maybe your teacher is using some special terminology, or maybe they just got it wrong. If you really want to clarify things with your teacher, draw some pictures so that everybody's clear on what you mean when you say "stretch by a factor of ..." Staecker (talk) 23:34, 8 December 2013 (UTC)
 * Also, it's not uncommon to use your definition; consider, for instance, the definition of scaled kernel under kernel density estimation, which is certainly (implicitly) "scaled by h". --Tardis (talk) 13:43, 11 December 2013 (UTC)