Plato, I read this in exactly the opposite- the OP knows and must deduce |sin(a)\le |a|. Of course, the definition of |a| is "|a|= a if and if x< 0". That should be sufficient.
Plato, I read this in exactly the opposite- the OP knows and must deduce |sin(a)\le |a|. Of course, the definition of |a| is "|a|= a if and if x< 0". That should be sufficient.