cos a + sin a - cos b + sin b = ?

Dear Student here use the formula , 
sina+sinb +(cosa-cosb)
= $$\begin{gathered} = 2\sin \left(\frac{\mathrm{a}+\mathrm{b}}{2}\right)\cos \left(\frac{\mathrm{a}-\mathrm{b}}{2}\right)-2\sin \left(\frac{\mathrm{a}+\mathrm{b}}{2}\right)\sin \left(\frac{\mathrm{a}-\mathrm{b}}{2}\right) \\ = 2\sin \left(\frac{\mathrm{a}+\mathrm{b}}{2}\right)\left[\cos \left(\frac{\mathrm{a}-\mathrm{b}}{2}\right)-\sin \left(\frac{\mathrm{a}-\mathrm{b}}{2}\right)\right] \\ \mathrm{Regards} \end{gathered}$$