"The red woman is dangerous, my lord."
Translation:Den røde kvinnen er farlig, min herre.
Why is in some cases the article explicitly used, while in others not? In this case, why would you choose to put 'den' at the beginning of the sentence, when it could technically be omitted?
Den/det/de is required when the definite noun is modified by an adjective.
Well technically it couldn't in this case ;) As you (might ;)) have learned in the lesson about adjectives "in addition to the noun transitioning into the definite form, an additional word is placed before the adjective in the definite form. This word changes depending on gender and number" This word being den/det/de.
So in this case woman is feminine and in the definite form, thus "den"