Fork me on GitHub
Math for the people, by the people.

User login

dihedral angle

% this is the default PlanetMath preamble.  as your knowledge
% of TeX increases, you will probably want to edit this, but
% it should be fine as is for beginners.

% almost certainly you want these

% used for TeXing text within eps files
% need this for including graphics (\includegraphics)
% for neatly defining theorems and propositions
% making logically defined graphics

% there are many more packages, add them here as you need them

% define commands here


Two distinct half-planes, emanating from a same line $l$, \PMlinkescapetext{divide} the space ($\mathbb{R}^3$) into two regions called {\em dihedral angles}.\, The line $l$ is the {\em edge} of the dihedral angle and the bounding half-planes are its {\em sides}.


The angle, which the sides of a dihedral planes separate from a normal plane of the edge, is the {\em normal section} of the dihedral angle.\, Apparently, all normal sections are equal.\, According to the \PMlinkescapetext{size} of the normal section, the dihedral angle may be called acute, right, obtuse, straight, \PMlinkname{skew}{ConvexAngle}, convex and concave.\, Unlike the angle between two planes, a dihedral angle may be over 90 \PMlinkescapetext{degrees}.

If two planes intersect each other and if one of the four dihedral angles formed is right, then also the others are right.\, Then we say that the planes are {\em perpendicular} to each other.