







Continuity on a closed interval 
20140921 

Pragya pose la question : The trouble I'm having is as follows :
a continuous function is most of the times defined on a closed interval,
but how is it possible to define it on a closed interval ,because to be continuous at endpoints of the interval the function's
limit must exist at that endpoint,for which it has to be defined in its neighborhood,but we don't know anything about whether the function is always defined in the neighborhood.
Please help... Penny Nom lui répond. 





Is a line lying in a plane an open or a closed region? 
20130213 

pardeep pose la question : please help with this question on the open and closed intervals ::
Is a line lying in a plane an open or a closed region? my teacher says it is a closed region reasoning out that it contains all it boundary points. please help how is it so? Harley Weston lui répond. 





Differentiable on an interval 
20100812 

Dave pose la question : Hi
I was wondering if a function can be differentiable at its endpoint. For example if I have Y = X^2 and it is bounded on closed interval [1,4], then is the derivative of the function differentiable on the closed interval [1,4] or open interval (1,4). They always say in many theorems that function is continuous on closed interval [a,b] and differentiable on open interval (a,b) and an example of this is Rolle's theorem. Thank you for your help. Robert Dawson lui répond. 





The extended real numbers 
20091102 

Justin pose la question : Hello there, I was wondering is the set of extended real numbers a closed set or an open set?
Justin Robert Dawson lui répond. 





The area enclosed by a curve and the xaxis 
20090104 

Rogerson pose la question : Find the area, S, enclosed by the curve y = x^2 + 6x  5 and the xaxis in the interval 0≤x≤4. Harley Weston lui répond. 





Open dots and closed dots 
20050929 

Cynthia pose la question : When graphing the solutions of an inequality, what is the difference between an open dot and a closed dot? Penny lui répond. 





A line from the center of the patch to the periphery 
20050101 

Sandrine pose la question : I am currently researching a patch disease of grasses. These patches are roughly circular. I need a term for a line from the center of the patch to the periphery. Since the patches are not perfectly circular, my supervisors tell me I cannot use the word 'radius'. What else could I use? Denis Hanson and Harley Weston lui répond. 





Finite differences 
20030210 

Jenny pose la question :
I need to find a formula that will work with any number. I am finding the volume of a 3d cross shape. Here are my results so far:
Term Number 0 1 2 3 4 5
nth term 1 7 25 63 129 231
1rst diff 6 18 38 66 102
2nd diff 12 20 28 36
3rd diff 8 8 8
I can't seem to find a formula that will work with any number. Any help would be much appreciated. Penny Nom lui répond. 

