I have been given the equation:
6xy^3+cos(y)+(2kx^2y^2-xsin(y)+y dy/dx=0
I need to
(a) find the value of k that will make the equation exact.
(b) Find an implicit solution when y(0)=1
There is an extra "(" in your equation. If I drop it I have [tex]6xy^3+ cos(y)+ 2kx^2y^2- xsin(y)+ ydy/dx= 0.
"Multiplying" the entire equation by dx gives
.
An equation of the form M(x,y)dx+ N(x,y)dy= 0 is "exact" if and only if
Here so [tex]M_y= 18xy^2- sin(y)+ 6kx^2y^2- xcos(y)[tex] while so . There is NO value of k that will make that exact.
Did you mean ?
In that case so and so . Those will be equal and the equation will be exact if 4k= 18 or if k= 9/2.
In that case, there exist F(x,y) such that . We must have . Integrating that with respect to x while holding y constant, . The "constant of integration", since we are holding y constant, may be some function of y, p(y).
Now, differentiating that with respect to y, and that must be equal to which, since k= 9/2 says so that everything involving x cancels (as it must) and we have p'(y)= y. From that where C now really is a constant.
Then .
The original equation says that dF= 0 which means F is equal to a constant: and, combining the fractions, .