(2y−2x2)dy+(y2+4xy)dx=0
Equation in total differentials μ(x,y)M(x,y)dy+μ(x,y)N(x,y)dx=0
where M(x,y)=2y−2x2 and N(x,y)=y2+4xy
Check for full differential: M(x,y)x′=−4x=2y+4x=N(x,y)y′
Search for an integrating factor μ(x,y)?M(x,y)x′=∂x∂M and N(x,y)y′=∂y∂N From condition: M∂x∂μ−N∂y∂μ=μ(∂y∂N−∂x∂M)
Let μ(x,y)=μ(y)⇒∂x∂μ=0 then the condition becomes: μ1dydμ=−N1(∂y∂N−∂x∂M) where right side - function from y
∫μdμ=∫−N1(∂y∂N−∂x∂M)dy=∫−y2 dy=−2ln(y)ln(μ)=−2ln(y)⇒μ=y21
Multiply the differential equation by y21
(y2−y22x2)dy+(y4x+1)dx=0, lost when dividing solution: y21→y=0
Equation in total differentials M(x,y)dy+N(x,y)dx=0
where M(x,y)=y2−y22x2 and N(x,y)=y4x+1
Check for full differential: M(x,y)x′=N(x,y)y′=−y24x
Find F(x,y):dF(x,y)=Fy′dy+Fx′dx
F(x,y)=∫N(x,y)dx=∫y′y4x+1 dx=y2x2+x+Cy(y2x2+x)y′=−y22x2Cy=∫M(x,y)−(y2x2+x)y′dy=∫y2 dy=2ln(y)F(x,y)=y2x2+x+Cy=2ln(y)+y2x2+x
Thus, the solution is 2ln(y)+y2x2+x=C
Comments