1. The problem statement, all variables and given/known data If f(x) = x ln (1+x), find an approximation for the increase in f(x) when x increases by δx. Hence estimate the value of ln (2.1), given that ln 2 = 0.6931. 2. Relevant equations δy ≈ (dy/dx)δx 3. The attempt at a solution δy ≈ [ln (1+x) + x/(1+x)] δx When x = 1, x ln(1+x) = ln 2 ≈ 0.6931 I would like to find a value for x such that x ln(1+x) = 2.1 However, I am unable to solve this equation. Also when I try to derive the value of δx from the answer given in my text book , 0.72, I get 0.040931534, which is not a solution to x ln(1+x) = 2.1 So i'm a bit stuck, and would appreciate any help someone might be able to offer.