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Question

What procedure should you use to fit each integrand to the basic integration rules? Do not integrate. (a) 2+xx2+9dx\int \frac{2+x}{x^{2}+9} d x, (b) cot2xdx\int \cot ^{2} x d x.

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a)

To solve\textbf{To solve} this integral we will apply linearity:

This menas\textbf{This menas}:

2+xx2+9 dx=21x2+9 dx+xx2+9 dx\begin{align*} \int{\frac{2+x}{x^2+9}\ dx}&=2\int{\frac{1}{x^2+9}\ dx} +\int{\frac{x}{x^2+9}\ dx}\\ \end{align*}

Now\textbf{Now}, we can see that we have basic integrals, but since we aren't asked we won't solve that.

Thus\textbf{Thus}, we have just:

Applied linearity\boxed{\textcolor{#c34632}{\text{Applied linearity}}}

b)

To solve\textbf{To solve} this integral we will apply the rule:

cotx=cosxsinx\color{#c34632}{\cot{x}=\frac{\cos{x}}{\sin{x}}}

This leads\textbf{This leads} to:

cot2x dx=cos2x1sin2xsin2x dx=1sin2xsin2x dx=1sin2x dxdx\begin{align*} \int{\cot^2{x}\ dx}&=\int{\frac{\overbrace{\cos^2{x}}^{1-\sin^2{x}}}{\sin^2{x}}\ dx}\\ &=\int{\frac{1-\sin^2{x}}{\sin^2{x}}\ dx}\\ &=\int{\frac{1}{\sin^2{x}}\ dx}-\int{dx}\\ \end{align*}

Now\textbf{Now}, we can just use basic rules for integrals ...

Thus\textbf{Thus}, our final solution\textbf{final solution} is:

$\boxed{\textcolor{#c34632}{\text{Apply trigonometric formula for cotx\cot{x} and llinearity}}}$

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