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Wednesday, April 9, 2014

Finding Equation - Curve, 13

Category: Differential Equations, Integral Calculus, Analytic Geometry, Algebra

"Published in Newark, California, USA"

Find the equation of the curve for which y" = 6x², and which passes through the points (0, 2) and (-1, 3).

Solution:

The concavity of a curve is equal to the second derivative of a curve with respect to x. In this case, y" = d²y/ dx². Let's consider the given concavity of a curve



We can rewrite the above equation as follows 



Multiply both sides of the equation by dx, we have




Integrate on both sides of the equation, we have






Since the slope of a curve is not given in the problem but the two points are given, then we have to continue the integration until we get an equation in terms of x and y. Let's consider the equation above


Multiply both sides of the equation by dx, we have




Integrate on both sides of the equation, we have







In order to get the value of arbitrary constants, we need to use the coordinates of two points so that we can form the two equations, two unknowns. 

By using the point (0, 2), substitute the value of x and y to the above equation, we have





By using the point (-1, 3), substitute the value of x and y to the above equation, we have





but


then the above equation becomes







Therefore, the equation of a curve is