略解(ここで r の方程式は全て特性方程式であり,y1 は余関数,y0 は特殊解,C1,C 2 は任意 定数である。) (1) r 2 3r 2 0 (2) r 2 8r 16 0 (r 2)(r 1) 0, r 2, 1 (r 4) 2 0, r 4 y C1e 2 x C2 e x y (C1 x C2 )e 4 x (3) r 2 2r 5 0 (4) r 2 20 0 r 1 (1) 2 5 1 2i (r 2 5i )(r 2 5i ) 0, r 2 5i y e x (C1 cos 2 x C2 sin 2 x) y C1 cos 2 5 x C2 sin 2 5 x (5) r 2 r 2 0 (6) r 2 2r 3 0 (r 2)(r 1) 0, r 2, 1 (r 3)(r 1) 0, r 3, 1 y1 C1e 2 x C2 e x y1 C1e 3 x C2 e x y0 ax b y0 ax 2 bx c dy 0 d 2 y0 a, 0 dx dx 2 2ax a 2b 2 x dy 0 d 2 y0 2ax b, 2a dx dx 2 3ax 2 (4a 3b) x 2a 2b 3c 9 x 2 11 2a 2, a 2b 0 a 1, b y0 x 1 2 1 2 y0 3x 2 4 x 1 y y1 y0 C1e 2 x C2 e x x 3a 9, 4a 3b 0, 2a 2b 3c 11 a 3, b 4, c 1 y y1 y0 1 2 (7) r 2 3r 2 0 (r 2)(r 1) 0, r 2, 1 y1 C1e 2 x C2 e x y0 a cos x b sin x dy0 a sin x b cos x, dx d 2 y0 a cos x b sin x dx 2 (a 3b) cos x (3a b) sin x 10 cos x a 3b 10, 3a b 0 a 1, b 3 y0 cos x 3 sin x y y1 y0 C1e 2 x C2 e x cos x 3 sin x C1e 3 x C2 e x 3x 2 4 x 1 (8) r 2 4 0 (r 2i )(r 2i ) 0, r 2i y1 C1 cos 2 x C2 sin 2 x y0 (ax b)e x dy 0 (ax a b)e x dx d 2 y0 (ax 2a b)e x 2 dx (5ax 2a 5b)e x 5 xe x 5a 5, 2a 5b 0 a 1, b 2 5 2 y 0 x e x 5 y y1 y0 2 C1 cos 2 x C2 sin 2 x x e x 5
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