User:Arowana77
Hello World！ The following is just a test.
![[asy] import three; unitsize(1cm); size(300); currentprojection=orthographic(-1/3,-1,-1/2); //basic coordinates to origin (-1,-1,-1) draw((-1,-1,-1)--(-1,-1,100)); draw((-1,-1,-1)--(-1,100,-1)); draw((-1,-1,-1)--(100,-1,-1)); label("$X$",(100,-1,-1), SW); label("$Y$",(-1,100,-1), SW); label("$Z$",(-1,-1,100), SW); // X+Y+Z=75 space over original (-1,-1,-1） draw((-1,-1,77)--(-1,77,-1),red); draw((77,-1,-1)--(-1,77,-1),red); draw((77,-1,-1)--(-1,-1,77),red); // draw((-1,38,38)--(77,-1,-1),red); draw((-1,-1,77)--(38,38,-1),red); //label label("$(-1,-1,77)$",(-1,-1,77), NW); label("$(-1,77,-1)$",(-1,77,-1), NW); label("$(77,-1,-1)$",(77,-1,-1), NE); label("$(25,25,25)$",(25,25,25), NE); label("$(-1,-1,-1)$",(-1,-1,-1),NW); label("$(-1,38,38)$",(-1,38,38),NW); label("$(38,38,-1)$",(38,38,-1),SE); //the target area in blue draw((-1,-1,77)--(25,25,25),blue); draw((-1,-1,77)--(-1,38,38),blue); draw((25,25,25)--(-1,38,38),blue); [/asy]](http://latex.artofproblemsolving.com/b/5/f/b5f33211644601fbe2ea9561007047d2a1c3c58e.png)
The area in BLUE is the space that satisfied the conditions, and it is 1/6 of a regular triangle.
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