0606 P22 - Nov 2020 - Q6 - 6 marks
8213
Find the exact value of
\(\int_2^4\frac{(x+1)^2}{x^2}\,dx.\)
Solution
Answer: \(\dfrac94+2\ln2\).
First expand the numerator:
\((x+1)^2=x^2+2x+1.\)
Therefore
\(\frac{(x+1)^2}{x^2}=1+\frac2x+\frac1{x^2}.\)
So
\(\int_2^4\frac{(x+1)^2}{x^2}\,dx =\int_2^4\left(1+\frac2x+\frac1{x^2}\right)\,dx.\)
An antiderivative is
\(x+2\ln x-\frac1x.\)
Evaluate between \(2\) and \(4\):
\(\left[x+2\ln x-\frac1x\right]_2^4.\)
This is
\(\left(4+2\ln4-\frac14\right)-\left(2+2\ln2-\frac12\right).\)
Since \(\ln4=2\ln2\), this becomes
\(2+2\ln2+\frac14.\)
Hence the exact value is
\(\frac94+2\ln2.\)