Find the exact value of the real number y. y = arcsec (-1)

Secant is a trigonometric function that quantifies the quotient of hypotenuse and the side that is adjacent to the given angle. This is the reciprocal of the cosine function. 
 
                   cosine = adjacent / hypotenuse = x/h
                      secant = h / x
Secant equal to -1 means that x and h are numerically equal but opposite in sign. 

                   secant = -1
                 cosine = 1/secant =1/-1 = -1
                     arccos (-1) = 180°
Thus, the answer to this item is 180°.