Answer
See below.
Work Step by Step
a) We see that $\sin u =\sin v =x$. It is a positive number.
and $\sin (u+v)=0$
Thus, $x+x \ne 0$
so, $2x \ne 0$
We see that $\sin u =\sin v =x$, and it is a positive number.
and $\sin (u-v)=-1$
Thus, $x-x \ne -1$
so, $0 \ne -1$
