Wednesday, June 10, 2015

A curve has dy/dx=3x^2-2x. The curve passes through the point (2;5). What is the equation of the curve?

To determine the equation of the curve, we'll have to
determine the antiderivative of the given expression.


Int
dy = Int (3x^2-2x)dx


We'll use the property of integrals to
be additive:


Int (3x^2-2x)dx = Int 3x^2 dx - Int
2xdx


Int (3x^2-2x)dx = 3 Int x^2dx - 2Int
xdx


Int (3x^2-2x)dx = 3*x^3/3 - 2*x^2/2 +
C


We'll simplify and we'll
get:


Int (3x^2-2x)dx = x^3 - x^2 +
C


What we've get is not a curve, but a family of curves
that depends on the values of the constant C.


We know, from
enunciation that the point  (2 , 5) is located on the curve. Therefore it's coordinates
will verify the equation of the curve.


5 = (2)^3 - (2)^2 +
C


5 = 8 - 4 + C


5 = 4 +
C


C = 5 - 4


C =
1


The equation of the curve, whose derivative
is dy/dx=3x^2-2x, is: y =  x^3 - x^2 + 1.

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