大学常微分dy/dx=cos(x-y)

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大学常微分dy/dx=cos(x-y)

大学常微分dy/dx=cos(x-y)
大学常微分
dy/dx=cos(x-y)

大学常微分dy/dx=cos(x-y)
令y-x=t,
dy/dx=d(x+t)/dx=1+dt/dx=cost;
dt/dx=cost-1;
dt/(cost-1)=dx;(x/=y)
即dt/[(-2sin^2(t/2))]=dx;
-1/2*csc^2(t/2)dt=dx;
两边积分后,-1/2*(-cot(t/2))=x+c;
即1/2*cot(y-x)=x+c
cot(y-x)=2x+c;
或者x=y;也可以.

等式左右两端对x求导:
d(ysin x-cos(x-y))/dx=d0/dx
dy/dx*sinx+y*cosx-dcos(x-y)/d(x-y)*d(x-y)/dx=0
y'sinx+ycosx+sin(x-y)(1-dy/dx)=0
y'sinx+ycosx+sin(x-y)-y'sin(x-y)=0
y'(sinx-sin(x-y))=-ycosx-sin(x-y)
y'=-(ycosx+sin(x-y))/(sinx-sin(x-y))

设x-y=t
d(x-t)/dx=cost
1=cost
t=0
x=y