## Encyclopedia > February 9

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# February 9

February 9 is the 40th day of the year in the Gregorian Calendar. There are 325 days remaining, 326 in leap years.

 Semi-norm ... norm. $\|x\|_\infty = \max \left(|x_1|, \ldots ,|x_n| \right).$ The concept of unit circle (the set of all vectors of norm 1) is different in ...