1. The problem statement, all variables and given/known data The first equation on the uploaded paper converts to the last equation. 2. Relevant equations when i substitute ln (1-u)=-u-(1/2)(u^2) into the first equation, i can get the first term in (3rd equation). but the second term of the 3rd equation ? 3. The attempt at a solution I tried ln(1-u)= -u-(1/2)(u^2)-(u^3)/3, then by completing the square. yet cant get. i wonder is that any way that i not yet learn. please guide what to do. Thank you.