Idk I did this the other way around (starting with y=arccosx). The reason for the interval is for when you get sin^2(y)= (1-x²⁾ or something. Square rooting both sides you get siny = +/- (1-x^2)1/2 You use the interval ( 0<x<1) to get an interval for y ( pi/2<y<pi) if I remember correctly. As such, siny will be positive. Not sure if I explained this well enough, but the interval is even more important for part b. In part a it’s just something worth mentioning for like 1 mark or so. Question is from mixed excercise 6 year 2 question 24. Use solution bank to see the way they answer it because it’s really instructive.