The value of (tan1° tan2° tan3° ... tan89°) is
(tan1° tan2° tan3° ... tan89°)
This can be written as,
(tan1° tan2° tan3° ....... tan44° tan45° tan46° ..... tan87° tan88° tan89°)
= [tan1° tan2° tan3° ....... tan44° tan45° tan (90 – 44)° ..... tan(90° - 3) tan (90° - 2) tan (90° - 1)]
= (tan1° tan2° tan3° ....... tan44° tan45° cot 44° ..... cot3° cot2° cot 1°)
= 1
(Since tan and cot are reciprocals of each other, they cancel each other.)