I have always wondered how to make perfectly angled(by degrees) lines. Well at least in GIMP 2.8.2(And probably previous versions) such feature can be obtained by guide addition when using the measure tool(«Shift»+«M»):
by pressing «Ctr»+«Alt» and left mouse click on both nodes:
Then simply use the brush stroke on a path, using the guides' intersection as snap points.
Here is a video showing how to stroke a path.