Recent content by Brucezhou

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    How to prove the product of upper triangular matrices is upper triangular?

    This seems easy but when I tried to do this, the best way I came up with is to list all entries and then do the multiplication work. Is there any better ,clearer and more simple way to do the proof?
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    Are pq and qp always 3-cycles?

    Group is in the next chapter. Thank you very much. I am learning that chapter.
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    Are pq and qp always 3-cycles?

    Homework Statement In the text, the products pq and qp of the permutations (2 3 4) and (1 3 5) were seen to be different. However, both products turned out to be 3-cycles. Is this an accident? Homework Equations p=(3 4 1)(2 5) q=(1 4 5 2) where p and q are permutations The Attempt at a...
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    Rotational Motion and Torque: Solving for Angular Acceleration

    Thank you a lot. I have solved. First my Torque equation is wrong. It should be 1/2 WL cos(sita) since the weight is exerted in the middle. Then it should be 2/3*a(tangent)=g*cos(sita) 2/3*cos(sita)*a(tangent)=g*cos^2(sita) cos(sita)*a(tangent)=a(vertical to ground) which should be at least...
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    Rotational Motion and Torque: Solving for Angular Acceleration

    Could you suggest a way to solving the problem? I don't have a standard answer key and I don't know where I got wrong. I have published my method above
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    Rotational Motion and Torque: Solving for Angular Acceleration

    Let Wr cos(sita)=1/3 mr^2* dw/dt. Simplify it then get: 3g*cos(sita)=r*dw/dt
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    Rotational Motion and Torque: Solving for Angular Acceleration

    The question is the first part of Question 63. It is required to make a proof. What I was trying to do is to build a equation with Torque= Moment of Inertia * angular acceleration. But when it was simplified to 3g cos(sita)= r* dw/dt, it seems not easy to solve it, since both of sita and dw/dt...
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    Can the Sum of Natural Numbers Really Be -1/12?

    A professor in Cambridge University has showed his proof that the sum of natural number was equal to -1/12. The video can be found on the internet.Well, although the way to proof I think is really ridiculous, it could be a good way to building a new math model. Since we think the sum of natural...
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    How to solve this nonlinear differential equation

    I think I have to explain what I said in the question. Bernoulli method and integrating factor don't work since I've tried several times but failed. And now I don't want others to waste too much time in these two ways, so I typed those words. But if someone finds this question can be solved...
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    How to solve this nonlinear differential equation

    The question is to find the function involving variables x and y.
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    How to solve this nonlinear differential equation

    dy/dx=2x+y^2 By the way, methods of solving linear differential equation are useless, such as integrating factor and Bernoulli method.
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    What is the use of time dilation.

    I mean the application,such as because of the time dilation, humans can observe some particles which don't have long lifetime,and know it
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