When the price of complementary goods increases, the demand curve for those complementary goods typically shifts to the left, indicating a decrease in demand. This is because complementary goods are items that are often consumed together, so when the price of one good rises, consumers are likely to buy less of it and, as a result, will also buy less of its complementary good.
For instance, if the price of printers (a complementary good) increases, consumers may buy fewer printers, and as a result, they will also buy fewer ink cartridges (the complementary good). This shift would be reflected in a leftward shift of the demand curve for the complementary good.
In summary, the most likely effect on the demand curve of complementary goods due to an increase in the price of complementary goods is a leftward shift in the demand curve, indicating a decrease in demand.