How to repair a cracked concrete slab?

I bought a new home about a year ago and shortly after we moved in the foyer tile grout cracked going toward the kitchen and five kitchen tile cracked and also more cracked grout. I called the builder and he had the grout and tile replaced/repaired but now several months later I have the same problem. I started looking at the foundation and noticed a crack under the foyer area and one at the back of the house near the kitchen. Anyone know what needs to be done to repair this? Thanks everyone.