Friday, April 17, 2015

`dy/dx = 5e^(-x/2)` Use integration to find a general solution to the differential equation

 The given problem: ` (dy)/(dx) = 5e^(-x/2)`  is in form of a first order ordinary differential equation. To evaluate this, we may follow the variable separable differential equation: `N(y) dy= M(x)dx`


Cross-multiply `dx` to the other side, we get:


`dy= 5e^(-x/2)dx`


In this form, we may now proceed to direct integration on both sides:


`int dy= int 5e^(-x/2)dx`


For the left side, we apply basic integration property: `int (dy)=y` .


For the right side, we may apply u-substitution by letting: `u = -x/2` then `du =-1/2 dx` or `-2du= dx` .


Plug-in the values: `-x/2=u` and `dx=-2du` , we get:


`int 5e^(-x/2)dx=int 5e^(u)* (-2 du)`


                  ` =int -10e^(u)du`


Apply the basic integration property: `int c*f(x)dx= c int f(x) dx` .


`int -10e^(u) du=(-10) int e^(u) du`


Apply basic integration formula for exponential function:


`(-10)int e^(u) du= -10e^(u)+C`


Plug-in` u=-x/2` on` -10e^(u)+C` , we get:


`int 5e^(-x/2) dx=-10e^(-x/2)+C`


Combining the results from both sides, we get the general solution of differential equation as:


`y=-10e^(-x/2)+C`

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