tan x = –
, x lies in second quadrant.
Given, 
, x lies in 2nd quadrant
sec2x – tan2x = 1
(∵ x lies in 2nd quadrant)
∴ sin2x + cos2x = 1
5
tan x = –, x lies in second quadrant.
Given, , x lies in 2nd quadrant
sec2x – tan2x = 1
(∵ x lies in 2nd quadrant)
∴ sin2x + cos2x = 1