how does
$\displaystyle tan(\frac{5}{4}) = tan(\frac{1}{4})$
Thanks.
I believe that you meant to ask 'how does $\displaystyle tan(\frac{5\pi}{4})=tan(\frac{\pi}{4})$
Look at the graph of tan(x):
Tan - Wolfram|Alpha
It repeats itself every $\displaystyle \pi$ radians. Do you understand why this is the case?