the equation is - tan2 x + sec2 x = 1.
Left hand side identity : - tan2 x + sec2 x.
Trigonometric function : tan x = sin x / cos x,
Reciprocal identity : sec x = 1/cos x.
- tan2 x + sec2 x = - (sin x/cos x)2 + (1/cos x)2
= - sin2 x/cos2 x + 1/cos2 x
= (1 - sin2 x)/cos2 x
Pythagorean identity : sin2 x + cos2 x = 1 .
= cos2 x / cos2 x
= 1