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Property of join
Let $X$ be path-connected and $Y$ be arbitrary topological space. Then the join $X*Y$ is simply connected. $\textbf{Proof}.$ We use Van K...
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The first two limits of the following problem were proposed at VJIMC, 2005, Category I. The exact value of the last limit was proposed by a ...
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Let $A$ be a real matrix such that $A+A^2A^t+(A^t)^2=0$. Prove that $A=0$. $\textbf{Solution}.$ Multiply the given equation by $A^t$ from th...
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Evaluate $$\sum_{n=1}^{\infty}\frac{1}{2^n n^2}.$$ Proof. The function $$S(x):=\sum_{n=1}^{\infty}\frac{x^n}{ n^2}$$ is well defined for...
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