Qt creator Adding external library (still: Cannot open include file: 'GL/glew.h')

Question

I followed the instruction:

1. In the Projects pane, open the project file (.pro).
2. Right-click in the code editor to open the context menu and select Add

Answer 1

1. Open .pro file with Editor
2. Add directory of library in INCLUDEPATH += section

 Append ` \` at the end of library path 

3. Go to Build > Run qmake

4. Check if library has been included .