[理工] [工數]一階ODE
大家晚安,今天在幫同學算工數時卡到這題,請大家給點提示
題目:
y'+2y=f(x),y(0)=0,where f(x)=1 ,x在0~3(含0、3)
0 ,x大於3(不含3)
解答1:
我算出積分因子I(x)=e^(2x)後乘回去並作分部積分
ye^(2x)=(1/2)e^(2x)+C1 ,x在0~3(含0、3)
C2 ,x大於3(不含3)
接著帶入條件y(0)=0
y=(1/2)(1-e^-2x) ,x在0~3(含0、3)
困惑:C2不知道怎麼求,C2是在x大於3求出來的,現在卻要把x=0帶入,我困惑了...
且強制帶入後C2=0,跟解答的1/2[(e^6)-1]e^(-2x)不同...
先在這裡謝謝各位了= =
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