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Tuesday, August 5, 2014

Finding the Equation of a Curve, 16

Category: Differential Equations

"Published in Newark, California, USA"

Find the equation of a curve whose slope at any point is equal to - (y + 1)/(x + 1) and which passes through the point (0, 0).

Solution:

The slope of a curve is equal to the first derivative of a curve with respect to x. In this case, y' = dy/dx. Let's consider the given slope of a curve  

  

Multiply both sides of the equation by (x + 1)dx, we have 







Integrate on both sides of the equation, we have 




In order to get the value of arbitrary constant, substitute the value of the given point which is P(0, 0) to the above equation, we have   





Therefore, the equation of a curve is 


 

Monday, August 4, 2014

Finding the Equation of a Curve, 15

Category: Differential Equations

"Published in Newark, California, USA"

Find the equation of a curve whose slope at any point is equal to y/(y - x) and which passes thru the point (-1, 2).

Solution:

The slope of a curve is equal to the first derivative of a curve with respect to x. In this case, y' = dy/dx. Let's consider the given slope of a curve 



Multiply both sides of the equation by (y - x)dx, we have 







Integrate on both sides of the equation, we have




In order to get the value of arbitrary constant, substitute the value of the given point which is P(-1, 2) to the above equation, we have  





Therefore, the equation of a curve is 




 

Sunday, August 3, 2014

Separation of Variables - Arbitrary Constant, 5

Category: Differential Equations

"Published in Newark, California, USA"

Find the particular solution for


in which y = 1 when x = 0.

Solution:

Consider the given equation above


In order to separate dx and dy from other variables, divide both sides of the equation by (x + 1)(y + 1) as follows




Integrate both sides of the equation, we have 







Substitute the value of x and y in order to get the value of C as follows 





Therefore, the particular solution is