Friday, October 2, 2015

Definite integral of x^2/sqrt(x^3+1), between 2 and 3, gives=?

We'll apply Leibniz-Newton formula to evaluate the definite
integral:


Int f(x)dx = F(b) - F(a), where a and b are the limits of
integration.


First, we'll determine the indefinite integral. We'll
change the variable as method of solving the integral.


Int
x^2dx/sqrt(x^3 + 1)


We notice that if we'll put x^3 + 1 = t and
we'll differentiate, we'll get the numerator.


3x^2dx =
dt


x^2dx = dt/3


We'll re-write the
integral:


Int x^2dx/sqrt(x^3 + 1) = Int (dt/3)/sqrt
t


Int (dt/3)/sqrt t = (1/3)*Int dt/sqrt
t


(1/3)*Int dt/sqrt t = (1/3)*[t^(-1/2 + 1)/(-1/2 + 1)] +
C


(1/3)*Int dt/sqrt t = (2/3)*sqrt t +
C


Int f(x)dx = (2/3)*sqrt (x^3 + 1) +
C


We'll evaluate the definite integral, having as limits of
integration x = 2 and x = 3:


Int f(x)dx = (2/3)*sqrt (3^3 + 1) -
(2/3)*sqrt (2^3 + 1)


Int f(x)dx = (2/3)*(sqrt28 -
3)


Int f(x)dx = (2*sqrt28)/3 -
2


The definite integral of the function f(x) =
x^2/sqrt(x^3 + 1), is Int f(x)dx = (2*sqrt28)/3 - 2.

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