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(iii) Notice that f(x) lies between 4-3=1 and 4+3=7 inclusive. Solving for f(x)=k can be interpreted as drawing a horizontal like y=k and finding the number of intersections with the y=f(x) curve. Hence, if no solutions arise, there are no intersections, ie k>7 or k<1.
(iv) A function has an inverse if and only if it is either strictly increasing or decreasing. Try sketching out the graph, you should be able to see that maximum value of A= pi radians, because in between pi/2 and pi radians, the function is strictly increasing. Alternatively, you can find dy/dx= -3 cosx, which is > or equals to zero for the domain defined.
(v) Let y=4-3sinx, then making x the subject gives x= arcsin (4-y)/3
Doing the reflection in the y=x line gives inverse of g to be = arcsin (4-x)/3
Hence, when x=3, g^-1 (3) =arcsin (4-3)/3 =arcsin (1/3).
Hope this helps. Peace.
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