(sec(of theta)+1)(sec(of theta)-1)=tan^2(of theta)
(sec theta +1)(sec theta -1)
= sec^2 theta -1
= [1 - cos^2 theta]/cos^2 theta
= sin^2 theta/ cos^2 theta
= tan^2 theta
= sec^2 theta -1
= [1 - cos^2 theta]/cos^2 theta
= sin^2 theta/ cos^2 theta
= tan^2 theta