What is the difference between "أعددنا لهم" (We have prepared for them) and "أعتدنا لهم" (We have made ready for them) as وردت (they appear) in the Holy Quran, and why are they وردت (mentioned) in two different forms?

There is no difference in meaning between "أعتدنا" (aʿtadnā) and "أعددنا" (aʿdadnā), as both mean "we have prepared." There is a difference of opinion regarding the origin of the two words. Some say that the origin of "أعتدنا" is "أعددنا," where the first letter dal was replaced with a ta. Others say the opposite. And there is an opinion that each of them is an independent root. The word "أعددنا" (aʿdadnā) has not been mentioned in the Holy Qur'an.