Wednesday, July 11, 2018

2xy' - ln(x^2) = 0 , y(1) = 2 Find the particular solution that satisfies the initial condition

The problem: 2xy'-ln(x^2)=0 is as first order ordinary differential equation that we can evaluate by applying variable separable differential equation:
N(y)y'=M(x)
N(y)(dy)/(dx)=M(x)
N(y) dy=M(x) dx
Apply direct integration: intN(y) dy= int M(x) dx to solve for the
 general solution of a differential equation.
Then, 2xy'-ln(x^2)=0 will be rearrange in to 2xy'= ln(x^2)
Let y' = (dy)/(dx) , we get: 2x(dy)/(dx)= ln(x^2)
or2x(dy)= ln(x^2)(dx)
Divide both sides by x to express in a form of N(y) dy=M(x) dx :
(2xdy)/x= (ln(x^2)dx)/x
2dy= (ln(x^2)dx)/x
Applying direct integration, we will have:
int 2dy= int (ln(x^2)dx)/x
For the left side, recall int dy = y then int 2dy = 2y
For the right side, we let u =x^2 then du =2x dx or dx=(du)/(2x) .
int (ln(x^2))/xdx=int (ln(u))/x*(du)/(2x)
                    =int (ln(u)du)/(2x^2)
                    =int (ln(u)du)/(2u)
                    =1/2 int ln(u)/u du
 
Let v=ln(u) then dv = 1/udu ,we get:
1/2 int ln(u)/u du=1/2 int v* dv
Applying the Power Rule of integration: int x^n dx = x^(n+1)/(n+1)+C
1/2 int v* dv= 1/2 v^(1+1)/(1+1)+C
                    = 1/2*v^2/2+C
                   =1/4v^2+C
Recall v = ln(u) and u = x^2 then v =ln(x^2) .
The integral will be:
int (ln(x^2))/xdx=1/4(ln(x^2))^2 +C or(ln(x^2))^2 /4+C
Combing the results from both sides, we get the general solution of the differential equation as:
2y = (ln(x^2))^2 /4+C
or y =(ln(x^2))^2 /8+C
 
To solve for the arbitary constant (C), we consider the initial condition y(1)=2 
When we plug-in the values, we get:
2 =(ln(1^2))^2 /8+C
2 =0/8+C
2=0+C
then C=2
.Plug-in C=2 on the general solution: y =(ln(x^2))^2 /8+C , we get the
particular solution as:
y =(ln(x^2))^2 /8+2

No comments:

Post a Comment

Summarize the major research findings of "Toward an experimental ecology of human development."

Based on findings of prior research, the author, Bronfenbrenner proposes that methods for natural observation research have been applied in ...