Recent content by JPC

Hello I am a student in CPGE (Classes Preparatoires aux grandes ecoles) in France (2nd year - specialisation Physics -chemistry) with another student, we are currently looking for information for our project on LEDs. We have to bring in our personal analysis to the subject, and go into the...

I saw on this page http://en.wikipedia.org/wiki/Compact_Disc : "The change in height between pits and lands results in a difference in intensity in the light reflected." : i do not really understand why, and i cannot find any details concerning this phenomena. The source also stated that the...

Thank you for the links and information Actually right now, in the end of our first year, we must search information and see what project we present next year on that theme The thing is, we have to make our projects very precise, they don't want the usual "talking" that everyone understands...

hello We are currently doing a TIPE Project on our first year of Prepa ( http://en.wikipedia.org/wiki/Classe_Pr%C3%A9paratoire_aux_Grandes_%C3%89coles ) We are thinking of doing our project on DVD/CD's (The theme is Surfaces), we would need to explain with precision how the encryption is made...

oh, this is not what i would write, first of all because i am in France ( i would write it in french), and finally because i just quickly resumed it here. I will of course clearly show i have verified all the hypothesis of the intermediate value theorem. And i better do, my maths professor is...

oh, i understand now, thank you :) if M(0) = a M(30) = b we have a+b = 5 we suppose 'a' different than 'b' M(t) continuous on the interval [0, 30] so there exists a 't' belonging to R where M(t) = 2.5

sorry for the late reply, i had an exam, 1 oral test, 2 big homeworks in between :D Hum, yes we have M(0) + M(30) = 5 one is necessarily bigger than the other if they are not equal. But then, if one is bigger than the other, how do you justify that there is a 30minutes time interval during...

Homework Statement Hello Its a pretty tricky question ! Help me find the answer so i can finally sleep (i only get the answer when i hand in the question sheets in 3 weeks) :D ->>>> You walk for 1 hour, and do 5 miles during that hour Question : show that there exist a time...

yes thank you Sisplat, that works very well :) I was looking for very complicated things, and i did a little confusion, thinking that the "^i" was associated to the multiply law and not the * law And yes, you were right, there were too many data given, to confuse you probably Thanks again

oh, i should have precised, here "*" is not necessarily the multiply law, it can be any law that respects the given conditions i tried with your method, putting to the square after, but then i end up working with 4 laws at the same time :D Thank you for the indication anyways, i have to...

Homework Statement (G, *) is a group (where * is a law) And for all 'i' belonging to {2, 3, 4}, for all (x, y) belonging to G2 (x * y) ^ i = (x^i) * (y^i) (where ^ is the law : to the power of) Question : Show that G is an Abelian (commutative) group Homework Equations The...

ok, thank you, you helped me save time not doing a long and incorrect maths demonstration :)

ok thank you then i must reply false to the proposition "if taking any 3 Real numbers (a, b, c), we have at least 2 of the same sign", because with (0, 0, 0) for example , we have none of the same sign

Homework Statement Hi I have to say true or false, and then demonstrate my answer "if taking any 3 Real numbers (a, b, c), we have at least 2 of the same sign" For me its true, i was thinking of creating a triplet (x, y, z), where x=1 if "a" positive, x=0 if "a" negative, same for y...

Thank you but from there how do i find the two values of 't' in E=[0, Pi/2] ? by looking at the graph, with x=0.5 and x=-0.5, its easy to say the two values of t for E=[0, Pi/2] are : Pi/15 and 2Pi/15 (once i have the (x, y) coords of these 2 double points, its easy to get those of the 2 others...