Therefore, it is an excellent approximation to write q (T) as 9ro (7) = (21 + 1)e-0. "(+1)/dj This integral is easy to evaluate because if we let x = J(J + 1), thendx = (2J + 1)d J and q (T) becomes 9rot (T) = emax/T dx 0 T (18.34) h2 rot Evaluate integral to to arrive at eq. 18.34