(tan 1°× tan2° × tan3°.................. tan89°) -এর মান নির্ণয় করি।

\((tan⁡ 1° ×tan⁡ 2° ×tan⁡ 3° ……..tan⁡ 89° ) \)
\(=tan⁡ 1° ×tan⁡ 2° ×tan⁡ 3° …×tan⁡ 44° \)
\(×tan⁡ 45° ×tan⁡ 46° …..tan⁡ 88° ×tan⁡ 89° \)
\(=tan⁡ 1° ×tan⁡ 89° ×tan⁡ 2° ×tan⁡ 88° \)
\(×….×tan⁡ 44° ×tan⁡ 46° ×tan⁡ 45° \)
\(=tan⁡ 1° ×tan⁡(90°-1°)×tan⁡ 2° ×tan⁡(90°-2°) \)
\(×…×tan⁡ 44° ×tan⁡ (90°-44°)× tan⁡ 45° \)
\(=tan⁡ 1° ×cot⁡ 1° ×tan⁡ 2° ×cot⁡ 2° ×….×tan⁡ 44° \)
\( ×cot⁡ 44° ×tan⁡ 45° \)
\(=1×1×…×1×1 [∵tan⁡θ×cot⁡θ=1] \)
\(=1 \) (Answer)