If tanα = mm+1 and tanβ = 12m+1, then α + β =
[IIT 1978; EAMCET 1992; Roorkee 1998; JMI EEE 2001]
We have, tan α = mm+1 and tan β = 12m+1
We know tan(α+β) = tanα+tanβ1−tanαtanβ
= mm+1+12m+11−m(m+1)1(2m+1) = 2m2+m+m+12m2+m+2m+1−m
= 2m2+2m+12m2+2m+1 = 1 ⇒ tan(α + β) = tan π4
Hence, α+β = π4.
Trick: As α+β is independent of m, therefore put m = 1,
then tanα = 12 and tanβ = 13. Therefore,
tan(α+β) = (12)+131−(16) = 1. Hence α + β = π4.
(Also check for other values of m).