Common mistakes
The second and third radicals are the same letter. They merge: رَدَّ: and come apart again before a consonant ending: رَدَدْتُ.
اِمْتَدَدَ → اِمْتَدَّ Past: heاِمْتَدَدَتْ → اِمْتَدَّتْ Past: sheاِمْتَدَدُوا → اِمْتَدُّوا Past: they (m.)يَمْتَدِدُ → يَمْتَدُّ Present: he