There was a Newsday article published about the errors on the test, and the focus was on #19. Some had commented on the online version of the article saying that inverse cosine doesn't have to be a function; however, we can go to the NYSDOE Glossary for grades 9-12 to see that assertion is false, even according to the state:
(Page 42) inverse trigonometric functions (A2T) Given the value of a trigonometric function for an angle ?, the inverse trigonometric function outputs the measure of angle ?. The inverses of the six basic trigonometric functions are written as sin-1, cos-1, tan-1, csc-1, sec-1, and cot-1.
While that is a lousy definition, the state is clearly defining the ^-1 notation as the inverse function. None of the choices in #19 is a function. I happen to know the people at Stony Brook University in the Newsday article personally and ALL are fantastic mathematicians and teachers and would not lead us astray.