as f(x) is continous at pi/4 .. so LHL = RHL at x=pi/4
==> pi/4 + √2.α.1/√2 = 2.pi/4.1 - β
==> α+β = pi/4
==> tan(α+β) = 1
==> tanα+tanβ = 1-tanαtanβ .... (1)
now (1+tanα)(1+tanβ) = 1+tanα+tanβ+tanαtanβ = 2 [tanα+tanβ+tanαtanβ =1 from (1)]