Evaluate the following integral:


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




2x – 3 = A(x + 1)(2x + 3) + B(x – 1)(2x + 3) + C(x – 1)(x + 1)……(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


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


– 5 = 0 – 2B + 0



Now put x = 1 in equation (ii), we get


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


– 1 = 10A + 0 + 0



Now put in equation (ii), we get





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 – 1 dy = dx and


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,



9