The input energy X is used to create the conditions of high temperature and pressure that are needed for fusion to take place.
When fusion happens, two hydrogen atoms fuse together into one, losing a bit of mass in the process. The mass difference is converted into energy Y (using E=mc2).
In this case, Y was greater than X, so there was a net gain in useful energy.
When fusion happens, two hydrogen atoms fuse together into one, losing a bit of mass in the process. The mass difference is converted into energy Y (using E=mc2).
In this case, Y was greater than X, so there was a net gain in useful energy.