Evaluate: `int_(-pi//4)^(pi//4)x^3sin^4xdx` (ii) `int_( a)^asqrt((a-x)/(a+x))dx`

Explanation

To evaluate the given integrals, let's break down each problem step by step.

### Problem (i): Evaluate
\[ \int_{-\frac{\pi}{4}}^{\frac{\pi}{4}} x^3 \sin^4 x \, dx \]

**Step 1: Identify the integrand function**
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