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 Mar 10 comment How to find all possible pairs of the cells in a table excluding those from the same column and then replace the other element in the taken combination. So the total amount of combinations in the table should be the amount of combinations in a row multiplied twice for the amount of rows. Mar 10 comment How to find all possible pairs of the cells in a table excluding those from the same column it wasn't very clear, but I thought I got it. For me this There are two independent choices of a row, one for each of the columns chosen is not clear. What does it mean "the columns chosen"? I do not choose columns, except the columns to which each element from any combination belong. So I have understood it this way: suppose I took the first row. I can take all combinations of the elements in it. For each of this combinations I can take a corresponding one from the other rows by replacing the first or the second element with one from every other row, hence the choice of n / k rows Mar 10 comment How to find all possible pairs of the cells in a table excluding those from the same column thank you very much Mar 10 comment How to find all possible pairs of the cells in a table excluding those from the same column I would like to elaborate, if you don't mind. For each combination in a row, there are (n/k) combinations in the table which contain the first element of the chosen combination and (n/k) combinations which contain the second element. So the final amount is the amount of combinations multiplied twice for the amount of rows, according to the multiplication principle Sep 13 comment Software to easily draw 3d plots from functions it's funny, but as far as I remember, I actually resorted to GeoGebra in that situation, it is now installed on my desktop Feb 4 comment Does a complex number multiplication have a geometric representation and why? okay, thank you, so I've understood that the statement that a complex number can be represented by a vector is incorrect. Please correct me, if I'm wrong Aug 12 comment How to find a basis of an image of a linear transformation? @BenWest thanks to you and André Nicolas, now it seems clear to me. Aug 12 comment How to find a basis of an image of a linear transformation? could you please provide an example? Jul 30 comment reduction of $6xy + 8 y^2 -12x-26y + 11 = 0$ to canonical one of a second-order curve thank you, but the main confusing thing was why I was not able to get the correct coordinates of transformed system's origin. Jul 29 comment reduction of $6xy + 8 y^2 -12x-26y + 11 = 0$ to canonical one of a second-order curve sorry, but I missed the point. Could you please detail how can I get the right answer (that the given equation is an equation of a hyperbola, which is rotated and shifted to the point (-1,2))? Jul 29 comment reduction of $6xy + 8 y^2 -12x-26y + 11 = 0$ to canonical one of a second-order curve thank you, I did not know about this way. I'll try it asap. Jul 27 comment Could anybody provide a more detailed explanation of a tangent equation in its general form? thank you, it just did not come to my mind that ' symbol has a meaning of a derivative. And in the textbook this word was not mentioned Jul 27 comment how to prove $ax + by = cx + dy \implies a = c, b = d$? how you can be sure that if $x \neq 0, y \neq 0 \implies a - c = b - d$ ? Could you please detail this? Jul 27 comment how to prove $ax + by = cx + dy \implies a = c, b = d$? and what if both x and y are 1? Jul 27 comment how to prove $ax + by = cx + dy \implies a = c, b = d$? I think they are both supposed to be 1, cause I saw this in the proving of coordinate transformation formula. x and y are the orts of the x and y axes. Jul 26 comment How to find an equation of a plane perpendicular to two other planes and passing through a point possible duplicate of Find a plane that passes through a point and is perpendicular to 2 planes Jul 26 comment Plane parallel to two lines and goes through a point? please, accept the answer Jul 26 comment Determining the equation of a plane that contains one point and one line. @ZolTunKul so did you checked this? Two months have passed. May 8 comment Can somebody provide an explanation to the formula of a one elementary integral? @Artem, thank you very much! Mar 30 comment Please, I need a more detailed explanation of the particular solution of the problem with vectors @DonAntonio, thank you for the suggestion, I am from the former USSR and in our school this way of a solution of quadratic equations isn't taught. I never heard about it. Thanks.