how to repair crack in cement garage floor without making it worse?

The crack widened by itself unless he used expanding foam which is doubtful.

so should I just reseal it with cement?

All cement mixtures that contain water; will shrink after the water has been evaporated. Depending on how wide your crack is, and considering the expanse of concrete. You want to keep sections small enough to avoid cracks. There are various expasion joint materials that you can use to avoid unsightly future cracks, some of these include: expansion joints, control joints, and construction joints, they are used for various applications. Prior to filling certain cracks, dowels or small sections of rebars are drilled into existing concrete, before pouring the new slab to keep settlements under control, these are packed with none shrink grout that contain very little or no water.

------------------------------------- architecturalrealms.org

|> |> | | III |> /-|\ III i> | _|__|__III i ^ |>\______/III i ^^^ | !__!__III/\ ^^^^^ /\ ////|====IIII === /\/////|====IIII === | | ||||::::::IIII === | | |||| IIII ===

----------------------------------