Remark: In fact (9) has three solutions for 0 < " < "1, with "1 0:43, and only one for " > "1.
The solution which exists for all " > 0 is the one with expansion given in x2 in (14); the
solution with the expansion given in x1 in (14) disappears for " > "1; and the third solution
(see figure 2: the solid line is the graph of a two-valued function) cannot be obtained by
regular perturbation.
Exercise 1. Solve by perturbation
x2