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I’m stuck on a Calculus question and need an explanation.

1) Evaluate the following integral using trigonometric substitution. LaTeX: intfrac{x^2}{sqrt{9-x^2}}dx:

2) Evaluate the following integral using partial fraction decomposition. LaTeX: intfrac{8left(x^2+4right)}{xleft(x^2+8right)}dx:

3) Evaluate the following integral. LaTeX: int_0^{frac{pi}{3}}tan xsec^{frac{7}{4}}xdx: