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A body cools in a surrounding which is at a constant temperature of θ0. Assume that it obeys Newton's law of cooling. Its temperature θ is plotted against time t. Tangents are drawn to the curve at the points Pθ=θ1 and Qθ=θ2. These tangents meet the time axis at angles of ϕ2 and ϕ1, as shown

(a) tanϕ2ϕ1=θ1-θ0θ2-θ0                          (b) tanϕ2ϕ1=θ2-θ0θ1-θ0
(c) tanϕ1ϕ2=θ1θ2                                 (d) tanϕ1ϕ2=θ2θ1