help with 2 c3 qs

https://b3755649dbd1afe3db91a899c3b9837b22326254.googledrive.com/host/0B1ZiqBksUHNYMG14YWtobVJUUms/for-Edexcel/Solomon%20H%20QP%20-%20C3%20Edexcel.pdf

Q7c) Why can't I have 1 MINUS root x-4 ?

Q4b)
I got the answer, however, I used trial and error...
Mark scheme does it algebraically:
-1 = a+b
-5 = a-b
Why does the first equation have a +
and the second equation has a -

7c Because for the inverse function to exist, f(x) must be one-to-one so

f^{-1}(x)

can only have one value

4b

\text{cosec}\frac{\pi}{2}=1\text{ and }\text{cosec}\frac{3\pi}{2}=-1

(edited 8 years ago)

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