There is no brackets so I am not really sure what you want.
1-sec8x/1-sec4x=tan8x/tan4x
Are you asking for all real values of x given that: ??
I suppose that is what you want.
\(\frac{1-sec(8x)}{1-sec(4x)}=\frac{tan(8x)}{tan(4x)}\\ \)
https://www.wolframalpha.com/input/?i=((1-sec(8x))%2F(1-(sec(4x))))%3Dtan(8x)%2Ftan(4x)
I keep getting a different answer but I'd trust wolfram|alpha over me.