Given the following data points

$\backslash$table$[[x,0\mathrm{.}4,0\mathrm{.}9,1\mathrm{.}4,1\mathrm{.}9,2\mathrm{.}4,2\mathrm{.}9,3\mathrm{.}4,3\mathrm{.}9,4\mathrm{.}4,4\mathrm{.}9,5\mathrm{.}4,5\mathrm{.}9],[y,0\mathrm{.}7486,0\mathrm{.}2931,0\mathrm{.}9360,0\mathrm{.}6443,1\mathrm{.}4025,0\mathrm{.}4456,0\mathrm{.}0892,-0\mathrm{.}9523,-1\mathrm{.}0688,-1\mathrm{.}0506,-0\mathrm{.}4982,-0\mathrm{.}4433]]$

$($a$)$ Find the value of $c$ in the function $y=$csinx to fit the above data by using the least squares method.

$($b$)$ Plot the graph of the function and the data on the same axis.