\(∫\frac {xdx}{(x-1)(x-2)}\ equals\)
\(log|\frac {(x-1)^2}{x-2}|+C\)
\(log|\frac {(x-2)^2}{x-1}|+C\)
\(log|(\frac {x-1}{x-2})^2|+C\)
\(log|{(x-1)(x-2)}|+C\)
Let \(\frac {xdx}{(x-1)(x-2)}\) = \(\frac {A}{(x-1)}+\frac {B}{(x-2)}\)
x = \(\frac {A}{(x-2)}+\frac {B}{(x-1)}\) ...(1)
Substituting x = 1 and 2 in (1), we obtain
\(A = −1\ and\ B = 2\)
∴ \(\frac {x}{(x-1)(x-2)}\) = \(\frac {-1}{(x-1)}+\frac {2}{(x-2)}\)
⇒ \(∫\)\(\frac {x}{(x-1)(x-2)}dx\) = \(∫\)\([\frac {-1}{(x-1)}+\frac {2}{(x-2)}]dx\)
= \(-log\ |x-1|+2log\ |x-2|+C\)
= \(log|\frac {(x-2)^2}{x-1}|+C\)
Hence, the correct Answer is B
The number of formulas used to decompose the given improper rational functions is given below. By using the given expressions, we can quickly write the integrand as a sum of proper rational functions.
For examples,