Ik denk goed na.
Ik wil nadenken.
Ik heb nagedacht.
I think carefully.
Yes. nadenken splits into na + denken. In a main clause the prefix goes to the end: Ik denk goed na.
The perfect tense is "Ik heb nagedacht" — the -ge- slots between the prefix and the stem.
nadenken means "to think (about)". Example: Ik denk goed na. (I think carefully.)
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