الف) $1 - \cot^4 x = \frac{1}{\sin^4 x} - \frac{\cos^4 x}{\sin^4 x}$

ج) $2(\sin^6 x + \cos^6 x) - 3(\sin^4 x + \cos^4 x) = -1$

هـ) $\frac{1}{\sin^4 x} + \frac{1}{\tan^4 x} = 1 + \frac{2\cot^2 x}{\sin^2 x}$

ز) $\sin^2 y - \sin^2 x = \frac{1}{1 + \tan^2 x} - \frac{1}{1 + \tan^2 y}$

ط) $\frac{\sin^4 x - \cos^4 x}{\cos^2 x} = (1 + \tan x)(\tan x - 1)$

$\tan x + \cot x = \sqrt{\frac{1}{\sin^2 x} + \frac{1}{\cos^2 x}}$