If \alpha+\beta=\pi/4, then simplify (\tan\alpha+1)(\tan\beta+1)

Porter Mccullough

Porter Mccullough

Answered question

2022-04-23

If α+β=π4, then simplify (tanα+1)(tanβ+1)

Answer & Explanation

j3jell5

j3jell5

Beginner2022-04-24Added 17 answers

1=tan(α+β)={tanα+tanβover1tanαtanβ}
so tanα+tanβ=1tanαtanβ .It follows that
(tanα+1)(tanβ+1)=tanαtanβ+(tanα+tanβ)+1
=tanαtanβ+(1tanαtanβ)+1
=2
Remark: A quick way to arrive at 2 as the answer is to note that if there is an answer, then it should hold for all α and β subject to α+β=π4 ,hence in particular for α=0 and β=π4, for which (tanα+1)(tanβ+1)=(0+1)(1+1)=2. (If you want to adhere to the limits 0<α,β<π4, then take the limit as (α,β)(0,π4))

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