Wednesday, November 9, 2011

Find the antiderivative of the function y=ln^2x/x^2.

To determine the primitive of te given function, we'll
calculate the indefinite integral of the function.


Int (ln
x)^2dx/x^2


We'll replace ln x by
t.


ln x = t


x =
e^t


We'll differentiate both
sides:


dx/x = dt


Int (ln
x)^2dx/x^2 = Int t^2*e^(-t)dt


We'll solve the integral in
variable t using parts.


Int udv = u*v - Int
vdu


Let u = t^2 => du =
2tdt


dv = e^(-t) dt => v =
-e^(-t)


Int t^2*e^(-t)dt = -t^2*e^(-t) + 2Int
t*e^(-t)dt


We'll integrate again Int t*e^(-t)dt by
parts:


u = t => du =
dt


dv = e^(-t) dt => v =
-e^(-t)


Int t*e^(-t)dt = -t*e^(-t) + Int e^(-t)
dt


Int t*e^(-t)dt = -t*e^(-t) - e^(-t) +
C


Int t^2*e^(-t)dt = -t^2*e^(-t) + 2*[-t*e^(-t) - e^(-t)] +
C


Int t^2*e^(-t)dt = -t^2*e^(-t) - 2t*e^(-t) - 2e^(-t) +
C


Int t^2*e^(-t)dt = -t^2/e^t - 2t/e^t - 2/e^t +
C


Int t^2*e^(-t)dt = -(t^2 + 2t + 2)/e^t +
C


Int (ln x)^2dx/x^2 = -[(ln x)^2 + 2ln x + 2)/x +
C


The antiderivative of the given function is
F(x) = -[(ln x)^2 + 2ln x + 2)/x + C.

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