Show that $\displaystyle secA+tanA=tan(\frac{\pi}{4}+\frac{A}{2})$ and deduce a similar expression for $\displaystyle secA-tanA$

Hence find the surd form of the values of $\displaystyle tan\frac{7\pi}{12}$ and $\displaystyle tan\frac{\pi}{12}$

i have completed the first two parts, for the second i got the equality $\displaystyle tan(\frac{\pi}{4}-\frac{A}{2})$

now i only have the last part to do and i'm lost.