[問題] 工數2階微分
題目 y"+y=cosx+secx
Yh=C1cox+C2sinx
y1=cox y2=sinx Wronskian=1
u1=∫-sinx(cosx+secx)dx= -∫sinxcosxdx-∫sinxsecxdx
=(1/4)cos2x+lncosx
u2=∫cosx(cosx+secx)dx=∫cos^2xdx+x=(1/2)(x+sinxcosx)+x
=(3/2)x+(1/2)sinxcosx
Yp={-(1/4)cos2x+lncosx}cosx+{(3/2)x+(1/2)sinxcosx)sinx
為何解答給卻是
Y(x)=(C1+lncosx)cosx+(C2+(3/2)x)sinx
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