$
y = sec^2x - tan^2x
$

any help with this one much appreciated..

2. Note that: $\color{blue} \sec ^2 x = 1 + \tan ^2 x$

So: $y \ = \ {\color{blue}\sec^2 x} - tan^2 x \ = \ {\color{blue}(1 + \tan^2 x)} - \tan^2 x \ = \ 1$

3. Originally Posted by o_O
Note that: $\color{blue} \sec ^2 x = 1 + \tan ^2 x$

So: $y \ = \ {\color{blue}\sec^2 x} - tan^2 x \ = \ {\color{blue}(1 + \tan^2 x)} - \tan^2 x \ = \ 1$
thanks mate.