---

\(\sec^2 12°- \cfrac{1}{\tan^2⁡ 78°} \)
\(\sec^2 12°- \cfrac{1}{\tan^2⁡⁡ (90°-12°)} \)
\(\sec^2 12°- \cfrac{1}{\cot^2 12°} \)
\(=sec^2⁡ 12° -tan^2⁡ 12° \)
\(=1 \)(প্রমানিত)