First substitute a point in, it would be good to choose a point that is different for all of the graphs but subbing in
![](https://latex.codecogs.com/png.latex?\bg_white \frac{\pi}{2})
is alright
so
![](https://latex.codecogs.com/png.latex?\bg_white \sin\left(\frac{\pi}{2}\right)=1)
hence
thus we can take out options A and B as they do not have the point.
now option C is just
![](https://latex.codecogs.com/png.latex?\bg_white \cos^{-1}(x))
so by deduction option D is the correct answer
the proper way to differentiate the two graphs are is to differentiate
![](https://latex.codecogs.com/png.latex?\bg_white \cos^{-1}(-\sin(x)))
which reveals that the gradient is a constant. Since there is a constant gradient, the graph must be straight, so the answer is D.