Thursday, January 4, 2018

int e^(sqrt(2x)) dx Find the indefinite integral by using substitution followed by integration by parts.

To evaluate the given integral problem int e^(sqrt(2x))dx us u-substituion, we may let:
u = 2x then du = 2 dx or (du)/2 = dx .
Plug-in the values u = 2x and dx = (du)/2 , we get:
int e^(sqrt(2x))dx =int e^(sqrt(u))* (du)/2
Apply the basic integration property: int c*f(x) dx = c int f(x) dx .
int e^(sqrt(u))* (du)/2=1/2 int e^(sqrt(u)) du
Apply another set of substitution, we let:
w = sqrt(u)
Square both sides of w =sqrt(u), we get: w^2 =u
Take the derivative on each side, it becomes: 2w dw = du 
Plug-in w =sqrt(u) and du = 2w dw , we get: 
1/2 int e^(sqrt(u)) du =1/2 int e^(w) * 2w dw
                                      = 1/2 * 2 inte^(w) *w dw
                                     = int e^w * w dw .
To evaluate the integral further, we apply integration by parts:int f* g' = f*g - int g *f'
Let: f =w then f' = dw
       g' = e^w dw then g = e^w
Applying the formula for integration by parts, we get:
int e^w * w dw = w*e^w - int e^w dw
                       = we^w -e^w +C
Recall we let: w =sqrt(u) and u = 2x then w =sqrt(2x) .
 Plug-in w=sqrt(2x) on  we^w -e^w +C , we get the complete indefinite integral as:
int e^(sqrt(2x))dx =sqrt(2x) e^(sqrt(2x)) -e^(sqrt(2x)) +C

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