\(\frac{sec(\beta)-1}{1-cos(\beta)}=sec(\beta)\)
we know that
\(sec(\beta)=\frac{1}{cos(\beta)}\)
then, lets replace it
\(\frac{\frac{1}{cos(\beta)}-1}{1-cos(\beta)}=\frac{1}{cos(\beta)}\)
multiple each member by \(cos(\beta)\)
\(\frac{1-cos(\beta)}{1-cos(\beta)}=1\)
simplifying
\(1=1\)
