I don't know how to show this:

If $\displaystyle x_{1}(s) = 2\arcsin(\frac{s}{4}) + 2\frac{s}{4}\sqrt{1-\frac{s^{2}}{16}} $

Then $\displaystyle x'_{1}(s)$$\displaystyle = \frac{1}{4}\sqrt{16-s^{2}} $

Can anyone help? Thanks.

Obviously you are just differnetiating first using the rule for differentiating arcsin but then once I evaluate it all I do not get the required solution.