This a question from complex number chapter of fp3

Find the following in the form a+ib, a,b member of real number set:

(a)

arccos 4 (b)

arcsin 2 (c)

arcsin i
I tried to these sums by: x=arccos4, so cosx=4, so e^(ix)-e^-(ix)=8

The answers:

(a) My answer:+/- i arcosh 4 Book's answer: 2m*pi +/- i arcosh 4 (b) My answer: +/- arcosh 2(i am not sure how i get that) Book's answer: (4m+1)*pi/2 +/- i arcosh 2 (c) My answer: i ln ((-2+/- sqrt 5)/2)) Book's answer: n*pi + i arsinh [(-1)^n]
So I gathered that I am missing something major here. Please anyone tell me the correct method to do these sums, thus enabling me to try it out myself. Just tell me the method, please

This is my first sums of this kind:woo:

P.s. i=imaginary.