Evaluate the following integral:

First we simplify numerator, we will rewrite denominator as shown below



Add and subtract numerator with ( – 6x2 + 11x – 6), we get





The denominator is factorized, so let separate the fraction through partial fraction, hence let




6x2 – 11x + 6 = A(x – 2)(x – 3) + B(x – 1)(x – 3) + C(x – 1)(x – 2)……(ii)


We need to solve for A, B and C. One way to do this is to pick values for x which will cancel each variable.


Put x = 1 in the above equation, we get


6(1)2 – 11(1) + 6 = A(1 – 2)(1 – 3) + B(1 – 1)(1 – 3) + C(1 – 1)(1 – 2)


1 = 2A + 0 + 0



Now put x = 2 in equation (ii), we get


6(2)2 – 11(2) + 6 = A(2 – 2)(2 – 3) + B(2 – 1)(2 – 3) + C(2 – 1)(2 – 2)


8 = 0 – B + 0


B = – 8


Now put x = 3 in equation (ii), we get


6(3)2 – 11(3) + 6 = A(3 – 2)(3 – 3) + B(3 – 1)(3 – 3) + C(3 – 1)(3 – 2)


27 = 0 + 0 + 2C



We put the values of A, B, and C values back into our partial fractions in equation (i) and replace this as the integrand. We get





Split up the integral,



Let substitute


u = x – 1 du = dx,


y = x – 2 dy = dx and


z = x – 3 dz = dx, so the above equation becomes,



On integrating we get



Substituting back, we get



Note: the absolute value signs account for the domain of the natural log function (x>0).


Hence,



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