Here's how to determine if the differential equations are exact and solve them.
a) (3x2y+ey)dx+(x3+xey−2y)dy=0
Step 1: Identify M(x,y) and N(x,y).
The differential equation is in the form M(x,y)dx+N(x,y)dy=0.
M(x,y)=3x2y+ey
N(x,y)=x3+xey−2y
Step 2: Check for exactness.
Calculate the partial derivatives ∂y∂M and ∂x∂N.
∂y∂M=∂y∂(3x2y+ey)=3x2+ey
∂x∂N=∂x∂(x3+xey−2y)=3x2+ey
Since ∂y∂M=∂x∂N, the differential equation is exact.
Step 3: Find the potential function F(x,y).
Integrate M(x,y) with respect to x, treating y as a constant:
F(x,y)=∫(3x2y+ey)dx=x3y+xey+g(y)
Now, differentiate F(x,y) with respect to y and set it equal to N(x,y):
∂y∂F=∂y∂(x3y+xey+g(y))=x3+xey+g′(y)
Equating this to N(x,y):
x3+xey+g′(y)=x3+xey−2y
g′(y)=−2y
Integrate g′(y) with respect to y to find g(y):
g(y)=∫−2ydy=−y2+C0
Substitute g(y) back into F(x,y):
F(x,y)=x3y+xey−y2+C0
The general solution is F(x,y)=C, where C is an arbitrary constant.
x3y+xey−y2=C
b) (siny−ysinx)dx+(xcosy+cosx)dy=0
Step 1: Identify M(x,y) and N(x,y).
The differential equation is in the form M(x,y)dx+N(x,y)dy=0.
M(x,y)=siny−ysinx
N(x,y)=xcosy+cosx
Step 2: Check for exactness.
Calculate the partial derivatives ∂y∂M and ∂x∂N.
∂y∂M=∂y∂(siny−ysinx)=cosy−sinx
∂x∂N=∂x∂(xcosy+cosx)=cosy−sinx
Since ∂y∂M=∂x∂N, the differential equation is exact.
Step 3: Find the potential function F(x,y).
Integrate M(x,y) with respect to x, treating y as a constant:
F(x,y)=∫(siny−ysinx)dx=xsiny−y(−cosx)+g(y)
F(x,y)=xsiny+ycosx+g(y)
Now, differentiate F(x,y) with respect to y and set it equal to N(x,y):
∂y∂F=∂y∂(xsiny+ycosx+g(y))=xcosy+cosx+g′(y)
Equating this to N(x,y):
xcosy+cosx+g′(y)=xcosy+cosx
g′(y)=0
Integrate g′(y) with respect to y to find g(y):
g(y)=∫0dy=C0
Substitute g(y) back into F(x,y):
F(x,y)=xsiny+ycosx+C0
The general solution is F(x,y)=C, where C is an arbitrary constant.
xsiny+ycosx=C
3 done, 2 left today. You're making progress.