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    Divergence operator in cylindrical & sherical

    look for some proof for the formula of the divergence operator in cylindrical & spherical coordinate is there any on the net ? TNX ! the formula here:
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    Negative volume ?

    negative volume ??? attached herewith pdf file with the problem and my solution .
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    Need help volume calculation .

    attached herewith : the problem with my attempt to solve it .
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    The generalization of Newton's 2nd Law to apply to variable mass systems

    F = dp/dt = d(mv)/dt = m(dv/dt) + v(dm/dt) = a + v(dm/dt) i dont understand why d(mv)/dt = m(dv/dt) + v(dm/dt) can somone help ? TNX !:smile:
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    Limit problem calculate

    need to calculate lim X->infinity of x*[1/x] , while [] represent floor function . TNX.
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    Volume problem

    hello ! need to find the volume of V: { x^2+y^2=z , x^4+y^4=1 } i dont know how to set up the triple integral caue i didnt find any way to understand the surface projection on the xy plane . I would appreciate any help ....
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    Problem with integrating factor

    what next ? TNX !
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    Calculate the limit of the series

    need to calculate the limit of the series (cos(a/n))^(n^3) n goes to infinity and a=!0 i try that : e^L L= the limit of (n^3)*ln(cos(a/n)) what now ??? TNX !
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    Sum of 1/ln(n)^(ln(n)) from n=3 to infinity?

    Sum of 1/ln(n)^(ln(n)) from n=3 to infinity? Does the sum of 1/ln(n)^(ln(n)) from n=3 to infinity converge or diverge? TNX ...............
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    Differential equation

    Homework Statement y`=(xy-y^2)/x^2 The Attempt at a Solution y` = y/x -(y/x)^2 {y/x=z , y=zx , y`=z+xz`} -z^2=x*dz/dx -z^2dx = xdz what`s next ? TNX . :smile:
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    Bounded function prove

    need to prove that f(x) bounded if f(x) continuous in [a,+infinite] and if theres a limit while x goes to +infinite. I would really appreciate any kind of help !
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    Unite series convergence

    thres two series An and Bn , Bn unite with An from some index. need to prove that limAn_k = limBn_m Bn_m and An_m are sub series . TNX !!!
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    Cauchy Criterion for Series limit

    need to prove theres limit by cauchy criterion the sequence: {X_n}=(10/1)(11/3).....(n+9/2n-1) my try : is that right ?
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    Cauchys criterion

    need to prove theres limit by cauchy criterion the sequence: {X_n}=(10/1)(11/3).....(n+9/2n-1) my try : is that right ?
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    How to calculate the limits ?

    how to calculate the limits ? appreciate any kind of help ...
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    Neeed help in prove

    need to prove that : between any two irrational numbers there is at least one rational number . TNX .
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    Prove question

    need to prove that if 0\leq X<n and also 0<n so x=0. The attempt at a solution assume that x>0 \exists n, x\ni(0,\infty) |n< x contradiction ! for X<0 theres contradiction agin . from here X have to be 0 is that right ?
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    Need help - problem newton laws + my try

    TNX ! [Broken]
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    Newton laws of motion

    what is the force work on object B in terms of a ? i know that the frictinon should be bigger than the force mBg for that the object will not fall down. but how to express it in terms of a ?? TNX .
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    Problem newton laws [Broken] the floor frictionless between D and C : MUs = 0.2 mA=5kg mB=10kg mD=2kg what is the value for Mc keepin MD in static position ? my effort : [Broken] the...
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    Acceleration proportion [Broken] how do i know what is the proportion between the acceleration of m1 and m2 ? TNX ...
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    One more newton laws

    Object A placed on a floor frictionless and object B placed on object A. The drag coefficient between A & B is 0.3 The length of A is 1m and the length of B is 30 cm . a force of 100N workin on object B. What is the time take to the edge of object B placed on the edge of object A ? all...
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    Contrary movement

    When 2 objects placed one on each other and one of them pulled, the second will move in a contrary way. there is a way to proof it with newtons law ??? tnx .:smile:
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    Problem newton laws

    A box put on a cart with velocity of 40m/s. The static drag coefficient between the box and the cart is 0.3. How long (in metes) before the cart stop should the driver start to slow down if he want to stop the cart on minimal time and make the box not move ? im received 544.2 m but the...