Question

i am unable to get the point here, tell what's done​

Answer 1

Answer:

we know,

$\sec {}^{2} \alpha - \tan{}^{2} \alpha = 1 \\ = > - ( \sec {}^{2} \alpha - \tan^{2} \alpha ) = - 1 \\ = > - \sec {}^{2} \alpha + \tan^{2} \alpha = - 1 \\ = > \tan {}^{2} \alpha - \sec {}^{2} \alpha = - 1$

here,

on the first step this has been done

this value has been put in the 2nd line....