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P_1 +2P_2+...+ nP_n= k1*x +k2 *x^2+k3*x^3...+kn*x^n but co . efficient of x^2,3,4,5...=0 (as shown in 2 case above) ---> P_1+2P_2+...+nP_n= kx ;) Ps: U can make it shorter by just using a general x^k and do the same as the case x^2k+1 :D

I think we can talk about electron moving in 1 direction in a magnetic field will experience a force resist to its motion(use a diagram)...Any1 got the answer for this ???

Q50:Use GP as UndertheSun: 1st one:GP with n+1 term common ratio = (1+x) ,then equal co. of x^r 2nd one : GP with n+1 term commonratio=(1+x)/x,then equal co. of x^r Q51: Consider co. of even power of x (x^2k) eg:X^2,4,6,8... P_1= - n!/(n-2k)!*(2k-1)! 2kP_2k= n!/(n-2k)!*(2k-1)! --->...

let @ be angle of..., T be tension w = 36*2(pi)/60=1.2(pi) rad/s Resolve horizontally: Tsin@= mw2r but r = lsin@ --> T sin@=mw2lsin@ --> T= 5*(1.2(pi))^2 * 1=71 N Resovle vertically : Tcos@=mg ---> cos@= mg/T= 5*9.8/71 --->@=46.36 degree

In ND solution: z1^2 + z2^2 +...+zn^2 = [Sum(zi)]^2 - 2Sum(zi*zj) eg: a2+b2+c2= (a+b+c)2 - 2(ab+bc+ac) ---> so U dont have to worry 'bout missing z1z3 or z1z4:D Btw do we need to prove this or just assume;)

I got Arnold-Arnold and Coroneos textbook but both of them dont have Proability( U can check that:D )...so can U guys give me some??? just post Ur question in this forum (and answer plz:) )

I really need some exercises with Proability ,can some 1 send me or show me a web site with this stuff.;) Thx in advance;)

study in class 'n do homework---> should take 'bout 5h/week:D .Anyway,I screwed up my English:(

Can we assume this or we need to prove it ( 2No. is ok but for n No...:( ) Btw,can we use stuff that they dont teach us here (since I've learned some good stuff in my country:D )

-Dissovle 5g salt in 20mL water -Put a PH probe in,record the result :D

In general, when U have a circular motion ,U need a centripetal force and in this case there 's no others than vertically gravity,and reaction force so Friction must be centripetal :D (Actually,when the object occupy circular motion it'll tend to fall out of the disc,'n the friction resist this...

To Survivor39: can U send me Ur essay too,plz??? I got 10/20 in essay for my trial(wish I can drop this crap :D) ps: pmed U my Email.Thx a lot ;)

Because I 've just been here for 1 year :D

92 :D rank7/195

I 've seen this1 in Year10Physics in my country:D Angular velocity of the object: w= 2*2(pi)/1=4(pi) Friction play the role of centripetal force in this case; and the greatest value for friction is Mmg (ortherwise it will slip out of the disc): Fc=mw2r=Mmg --> m*16*(pi)2*r=Mmg...

I dont understand why when t =0 ,x=-6.4:confused:

Oh,I forgot to count AC case in my solution:D ;anyway I redo it 'n got this: In 1B case there r 6 way In 3B case there r 12 way In 2Bs case there r 3 case: C is the 1st--->(CB) is 1st ,there're 3!/2!=3 C is the last---> (BC) is last, there're 3!/2!=3 C in the middle--> (BCB) is a...

---> I dont really understand what U meant(coz of mine bad English:D ). Anyway,if C is between As then they have touched<--??? Explain for 2B in mine solution: let AAC be in a group(for touching) the others r 2 B --> no.of way is 3!/2! 'n in AAC there 's 3!/2! no.of arrangement.--> No. of way A...

Hehe,for part 1: there're 3 cases:(not sure):D + 3 same,2 same (eg:3A,2B): 6* 5!/3!*2!=60 + 3 same,2 diff (eg:3A,1B,1C) : 3*5!/3!=60 + 2 same,2same,1 other (eg:2A,2B,1C) : 3*5!/2!*2!=90 --> Total=60+60+90=210

I dont really understand the question,anyway here is my answer: :D ( I guess the question want U have both A 'n C in the five,if not U just add all the case where there's 1 of A or C :p) If A cant touch C ,B must be in the five: + if 1 B: obviously there're 4 ways ...