Declension table of kartavya

Masculine	Singular	Dual	Plural
Nominative	kartavyaḥ	kartavyau	kartavyāḥ
Vocative	kartavya	kartavyau	kartavyāḥ
Accusative	kartavyam	kartavyau	kartavyān
Instrumental	kartavyena	kartavyābhyām	kartavyaiḥ
Dative	kartavyāya	kartavyābhyām	kartavyebhyaḥ
Ablative	kartavyāt	kartavyābhyām	kartavyebhyaḥ
Genitive	kartavyasya	kartavyayoḥ	kartavyānām
Locative	kartavye	kartavyayoḥ	kartavyeṣu

Compound kartavya -

Adverb -kartavyam -kartavyāt