已知方程y'=f(x,y)的通解为y=g(x,C)则方程________________的通解为y=exp[g(1/x,C)],方程__________的通解为y=[g(x^3,C)]^(1/5)标答为(x^2)y'=-yf(1/x,lny);5(y^4)*y'=3(x^3)f(x^3,y^5)
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已知方程y'=f(x,y)的通解为y=g(x,C)则方程________________的通解为y=exp[g(1/x,C)],方程__________的通解为y=[g(x^3,C)]^(1/5)标答为(x^2)y'=-yf(1/x,lny);5(y^4)*y'=3(x^3)f(x^3,y^5)
已知方程y'=f(x,y)的通解为y=g(x,C)
则方程________________的通解为y=exp[g(1/x,C)],方程__________的通解为y=[g(x^3,C)]^(1/5)
标答为(x^2)y'=-yf(1/x,lny);5(y^4)*y'=3(x^3)f(x^3,y^5)
已知方程y'=f(x,y)的通解为y=g(x,C)则方程________________的通解为y=exp[g(1/x,C)],方程__________的通解为y=[g(x^3,C)]^(1/5)标答为(x^2)y'=-yf(1/x,lny);5(y^4)*y'=3(x^3)f(x^3,y^5)
1.lny = g(1/x,C)
所以lny = g(1/x,C)是[lny]' = f(1/x,lny)的解
但需要特别注意的就是这里的y是1/x的函数,[lny]'是lny对(1/x)的导数,也就是dlny/d(1/x)
f(1/x,lny)=dlny/d(1/x)
= (1/y)*dy/d(1/x)
= (1/y)*(dy/dx)/[d(1/x)/dx]
= (y'/y)*(-x^2)
所以是(x^2)y'=-yf(1/x,lny)的解
2,y^5 = g(x^3,C)
所以是d(y^5)/d(x^3) = f(x^3,y^5)的解
f(x^3,y^5) = (5y^4dy)/(3x^2dx) = y'*(5y^4)/(3x^2)