tan² θ ( cosec² θ - 1) - cot² θ (sec² θ -1) এর মান কত ? 

$\begin{array}{l} \tan ^{2} \theta\left(\operatorname{cosec}^{2} \theta-1\right)-\cot ^{2} \theta\left(\sec ^{2} \theta-1\right) \\ =\tan ^{2} \theta \cdot \cot ^{2} \theta-\cot ^{2} \theta \cdot \tan ^{2} \theta \\ =1-1=0 \end{array}$