KöMaL 2014 B4628

Show that if $\alpha$, $\beta$ and $\gamma$ are the angles of a triangle then $\sin\alpha\cdot \sin\beta\cdot \cos\gamma+\sin\alpha\cdot \cos\beta\cdot \sin\gamma+ \cos\alpha\cdot \sin\beta\cdot \sin\gamma\le \frac 98$.