Concept:
For integrals containing powers of \((x-1)\) and \((x+2)\), a useful substitution is:
\(\displaystyle u=\frac{x-1}{x+2}\)
This is useful because the derivative of this fraction produces a factor involving \((x+2)^2\).
Step 1: Rewrite the integral.
\(\displaystyle I=\int \frac{1}{\sqrt[4]{(x-1)^3(x+2)^5}}\,dx\)
This can be written as:
\(\displaystyle I=\int (x-1)^{-\frac{3}{4}}(x+2)^{-\frac{5}{4}}\,dx\)
Step 2: Choose a suitable expression.
Let us check the derivative of:
\(\displaystyle \left(\frac{x-1}{x+2}\right)^{\frac{1}{4}}\)
Step 3: Differentiate the inner fraction.
Let,
\(\displaystyle u=\frac{x-1}{x+2}\)
Then,
\(\displaystyle \frac{du}{dx}=\frac{(x+2)(1)-(x-1)(1)}{(x+2)^2}\)
\(\displaystyle \frac{du}{dx}=\frac{x+2-x+1}{(x+2)^2}\)
\(\displaystyle \frac{du}{dx}=\frac{3}{(x+2)^2}\)
Step 4: Differentiate the complete expression.
\(\displaystyle \frac{d}{dx}\left[\left(\frac{x-1}{x+2}\right)^{\frac{1}{4}}\right]\)
\(\displaystyle =\frac{1}{4}\left(\frac{x-1}{x+2}\right)^{-\frac{3}{4}}\cdot \frac{3}{(x+2)^2}\)
\(\displaystyle =\frac{3}{4}(x-1)^{-\frac{3}{4}}(x+2)^{\frac{3}{4}}\cdot (x+2)^{-2}\)
\(\displaystyle =\frac{3}{4}(x-1)^{-\frac{3}{4}}(x+2)^{-\frac{5}{4}}\)
Step 5: Compare with the given integrand.
The given integrand is:
\(\displaystyle (x-1)^{-\frac{3}{4}}(x+2)^{-\frac{5}{4}}\)
We obtained:
\(\displaystyle \frac{d}{dx}\left[\left(\frac{x-1}{x+2}\right)^{\frac{1}{4}}\right]=\frac{3}{4}(x-1)^{-\frac{3}{4}}(x+2)^{-\frac{5}{4}}\)
Therefore,
\(\displaystyle (x-1)^{-\frac{3}{4}}(x+2)^{-\frac{5}{4}}=\frac{4}{3}\frac{d}{dx}\left[\left(\frac{x-1}{x+2}\right)^{\frac{1}{4}}\right]\)
Step 6: Write the final integral.
\(\displaystyle I=\frac{4}{3}\left(\frac{x-1}{x+2}\right)^{\frac{1}{4}}+C\)
Hence,
\(\displaystyle \boxed{\frac{4}{3}\left(\frac{x-1}{x+2}\right)^{\frac{1}{4}}+C}\)