geometry app question...

[Didier Lachieze]

Starting from your 3 lines you can then define the triangle vertices and draw the circle :
GA:= line(y = (2*x+5));
GB:= line(y = (-2*x-4));
GC:= line(y = (-7*x+5));
GD:= single_inter(GA,GB);
GE:= single_inter(GB,GC);
GG:= single_inter(GA,GC);
GH:= incircle(GD,GE,GG);

If you have just 3 points GA,GB,GC you can draw the triangle with triangle(GA,GB,GC)