OpenGL Backward compatibility

I have purchased a graphics card which supports OpenGL 4.2. But I want to develop an application which should support OpenGL 2.0

Does my card will support OpenGL 2.0 apps(Backward compatibility)?? Then how to ensure backwards-compatibility

I have planned to use GLUT/GLFW C++ libraries.

https://developer.nvidia.com/opengl-driver - please read about compatibility and that no 'old' functionality will be removed from the drivers.

In general you can create your application in two modes:

• Core: This is modern OpenGL, no fixed pipeline functionality. In freeGlut you can use glutInitContextFlags (GLUT_CORE_PROFILE); and glutInitContextVersion (4, 2); to use core opengl 4.2
• Compatibility: all functionalities from OpenGL 1.1 up to 4.2 (in your case) are supported and all those features can be used in your code. By default apps use this profile, or you can create it via glutInitContextFlags (GLUT_COMPATIBILITY_PROFILE );