Prove the following Inequality. Given that $\alpha,\beta$ and $\gamma\in (0,\pi)$ and $\alpha+\gamma+\beta=\pi$, show that $$\cos\alpha+\cos\gamma+\sin\beta\leq\frac{3\sqrt3}{2}.$$
Now I am aware of the following Inequality: $\cos\alpha+\cos\gamma+\cos\beta\leq\frac{3}{2}$, but notice that the term $\cos\beta$ has been replaced with $\sin\beta$. I also tried substituting $\sin\beta=\sin(\pi-(\alpha+\gamma))=\sin(\alpha+\gamma)$ and expanding the resulting expression but I was unable to deduce anything meaningful. 

$\cos(\alpha)+\cos(\gamma)+\sin(\beta)=\sin(\frac{\pi}{2}-\alpha)+\sin(\frac{\pi}{2}-\gamma)+\sin(\beta)$
1) Suppose $\beta \leq \frac{\pi}{2}$
Using Jensen inequality we get: $\frac{\sin(\frac{\pi}{2}-\alpha)+\sin(\frac{\pi}{2}-\gamma)+\sin(\beta)}{3} \leq \sin(\frac{\frac{\pi}{2}-\alpha+\frac{\pi}{2}-\gamma+\beta}{3})=\sin(\frac{2\beta}{3})$
Since $\frac{2\beta}{3}\leq \frac{\pi}{3}$, we get : $\cos(\alpha)+\cos(\gamma)+\sin(\beta) \leq 3 \sin(\frac{\pi}{3})=\frac{3\sqrt{3}}{2}$
1) Suppose $\beta \geq \frac{\pi}{2}$
Using Jensen inequality we get: $\frac{\sin(\frac{\pi}{2}-\alpha)+\sin(\frac{\pi}{2}-\gamma)}{2} \leq \sin(\frac{\frac{\pi}{2}-\alpha+\frac{\pi}{2}-\gamma}{2})=\sin(\frac{\pi-\beta}{2})$
Since $\frac{\pi-\beta}{2} \leq \frac{\pi}{4}$, we get : $\cos(\alpha)+\cos(\gamma)+\sin(\beta) \leq 2 \sin(\frac{\pi}{4})+\sin(\beta)=1+\sqrt{2}\leq \frac{3\sqrt{3}}{2}$ 
