(tana+1)(tanβ+1)=2
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tanαtanβ+tanα+tanβ+1=2
tanα+tanβ=1-tanαtanβ
∴tan(α+β)
=(tanα+tanβ)/(1-tanαtanβ)
=1
∴α+β=kπ+π/4,k∈Z