Question

1. cos^-1((-sqrt3)/2)

5pi/6

2. arccos(cos7pi/2)

-pi/2

3. sin^-1(sin7pi/4)

-pi/4

4. csc(arctan11/60)

61/11

Answer 1

1. ok
#2
why are you giving the negative result?
cos 7π/2 = 0
so we need cos^-1 (0) = π/2
see: http://www.wolframalpha.com/input/?i=arccos%28cos%287pi%2F2%29%29+

#4. arctan (11/60)
construct a right-angled triangle with opposite as 60 and adjacent as 11
r^2 = 11^2 + 60^2 = 3721
r = √3720
so sin(arctan (11/60)) = 11/√3720
then csc(arctan (11/60)) = √3720/11

Answer 2

For #4, why did you take the square root of 3720 when r^2 = 3721?