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y?x?a2x2?a3x3?a4x4
y2a2x?3?2a3x?4?3a4x2n(n?1)anxn?2
把 y及 y代入方程 yxy?0?得
2a2?3?2a3x?4?3a4x2n(n?1)anxn?2
x(x?a2x2?a3x3?a4x4anxn)?0?
即 2a2?3?2a3x?(4?3a4?1)x2?(5?4a5?a2)x3?
(6?5a6?a3)x4[(n?2)(n?1)an?2?an?1]xn0?