当α+β=45°时,有tanα+tanβ+tanα*tanβ=1
(1+tan21°)(1+tan22°)(1+tan23°)(1+tan24°)
=(1+ tan21°+tan24+°tan21°tan24°)( 1+tan22°+tan23°+ tan22°tan23°)
=(1+1)(1+1)
=4
当α+β=45°时,有tanα+tanβ+tanα*tanβ=1
(1+tan21°)(1+tan22°)(1+tan23°)(1+tan24°)
=(1+ tan21°+tan24+°tan21°tan24°)( 1+tan22°+tan23°+ tan22°tan23°)
=(1+1)(1+1)
=4