O } \frac{d^{2} x_{1}}{d t^{2}}-2 \frac{d x_{1}}{d t}-x_{1}=-\frac{d}{d t} F(t)+F(t) \text { } \frac{d^{2} x_{1}}{d t^{2}}+2 \frac{d x_{1}}{d t}+x_{1}=+\frac{d}{d t} F(t)+F(t) \left(\frac{d^{2} x_{1}}{d t^{2}}+2 \frac{d x_{1}}{d t}-x_{1}=-\frac{d}{d t} F(t)+F(t)\right. O \frac{d x_{1}}{d t}-x_{1}=F(t)
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