1. The problem statement, all variables and given/known data I have this equation: y = 5(1 - e-x) and I need to find its root. 2. Relevant equations I'm trying to go from planck's blackbody formula to wien's displacement law by taking the derivative of planck's blackbody formula with respect to wavelength and then setting it equal to 0 in order to find the maximum wavelength. 3. The attempt at a solution I know the correct answer because I found an old thread here where they found the intersection between y = x and this equation. However, I don't understand why that gives the correct answer, and I wouldn't know how to write that down as an answer for this homework problem.