Translation:The apple is sweet.
take a closer look at the "Hey". it appears only on the "apple" (התפוח). but not in the "sweet". in heb in order to definite a phrase we add "Hay" to the object and its adjective. if there is more that one adjective we also add "Ve" " before.
the apple is sweet = HaTapuach Matok || the sweet apple = HaTapuach HaMatok || the sweet red apple = HaTapuach HaMatok VeHaAdom
In a phrase like that both the noun and the adjective take the article – התפוח המתוק.
the sentence has to agree the both have to have a "ה" in front of the word: התפוח המתוק
Why is it written "התפוח" instead of "התפוך". Isn't that what ending letters are for?
There is no particular end letter for chet (ח), but there is one for qaf (כ/ך). They are sometimes pronounced the same.
Because in a phrase like yours both the noun and the adjective would take the article 'hey' – התפוח המתוק.