@Kitonum Thank you very much

@Carl Love You can restrict each side of each triangle to be integer or not.

@acer Thank you very much. My goal is expand the expression has the form (a + b)^n step by step. 

@acer Thank you very much. Let me try other special cases. 
Is this another question? Can your code use for this cases
(x + 3)^2 = x^2 + 2. (x)*(3) + 3^2 = x^2 + 6 x + 9;
(t- k)^2 = t^2 - 2*t*k + k^2?

@acer Please see this case L := [[1, 2], [-3,1]]; Can I write x instead 1 x or y instead 1 y?

@acer I am sory. Now I can save the file. 

@acer When I copy your code and put the the file in the same folder, I put a new name of the file, when I enter, I get the massage as below. How can I compile to get the results<

@acer Thank you very much.

@acer Can I get latex file in the same folder of the  Maple file instead copy from Maple?

@mmcdara I see here  https://mathematica.stackexchange.com/questions/306684/how-can-i-find-meandata-mediandata-quartilesdata-variancedata-standardde/306685#306685

@Kitonum Thank you very much. I don't know, by using your code for the S(0,0,sqrt(2)/2), the dihedral not equalt to 3*Pi/4. 

@mmcdara  Please note that "When the two intersecting planes", my quesiton is dihedral angle of two halfplanes. 

@Carl Love  Please note that "When the two intersecting planes", my quesiton is dihedral angle of two halfplanes. 

@Carl Love I want to calculate dihedral angle of two halfplanes not angle two planes, https://en.wikipedia.org/wiki/Dihedral_angle,  I think, the answers are 2*Pi/3 and 3*Pi/4. 

@Kitonum Thank you very much.