If θ=tan−1a,ϕ=tan−1b and ab=−1, then (θ−ϕ) is equal to
0
π4
π2
None of these
Given that, θ=tan−1a and ϕ=tan−1b and ab=−1 ∴tanθtanϕ=ab=−1⇒tanθ=−cotϕ⇒tanθ=tanπ2+ϕ⇒θ−ϕ=π2