Evaluate the following integral:

First we simplify numerator, we get







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




5x + 1 = A(x – 1) + B(x + 2)……(ii)


We need to solve for A and B. 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


5(1) + 1 = A(1 – 1) + B(1 + 2)


6 = 0 + 3B


B = 2


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


5( – 2) + 1 = A(( – 2) – 1) + B(( – 2) + 2)


– 9 = – 3A + 0


A = 3


We put the values of A and B 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 + 2 du = dx and z = x – 1 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,



4