Text Formatting ⇒ Showing error - in equationarray -

[sachinrajsharma]

Hi,
Good Day!

I have been trying the following source code but unable to get the output showing error " missing \endgroup inserted"

Code: Select all

$$\begin{eqnarray*}
\int_{0}^{\pi /2}f(x)dx &=&\int_{0}^{\pi /2}\sin ^{7}x\cos ^{5}xdx \\
&=&\int_{0}^{\pi /2}\sin ^{7}x\cdot \cos xdx-2\int_{0}^{\pi /2}\sin
^{9}x\cdot \cos xdx \\
&&+\int_{0}^{\pi /2}\sin ^{11}x\cdot \cos xdx \\
&=&\frac{1}{8}-2\cdot \frac{1}{10}+\frac{1}{12}=\frac{1}{120}.
\end{eqnarray*}$$

Please guide how to resolve this.

Regards,

Sachin Sharma

[Johannes_B]

Please, always provide a compilable and complete Minimal Working Example using the code-button. This makes testing much easier.

$$ are TeX-Syntax and not to be used with LaTeX. The right expression would be \[ E = mc^2 \].

The environment equationarray is not used anymore, use align instead.

Code: Select all

\documentclass{scrartcl}

\usepackage{mathtools}

\begin{document}
\begin{align}
\int_{0}^{\pi /2}f(x)dx &=&\int_{0}^{\pi /2}\sin ^{7}x\cos ^{5}xdx \\
&=&\int_{0}^{\pi /2}\sin ^{7}x\cdot \cos xdx-2\int_{0}^{\pi /2}\sin
^{9}x\cdot \cos xdx \\
&&+\int_{0}^{\pi /2}\sin ^{11}x\cdot \cos xdx \\
&=&\frac{1}{8}-2\cdot \frac{1}{10}+\frac{1}{12}=\frac{1}{120}.
\end{align}
\end{document} 

[cgnieder]

I like to repeat: {eqnarray} really should be avoided. Also, $$...$$ is plain TeX syntax and should not be used in a LaTeX document.

The &=& is {eqnarray} syntax and doesn't hold for {align} which uses &= instead. Also the splitted line beginning with + should at least be indented with \quad:

Code: Select all

\documentclass{scrartcl}

\usepackage{mathtools}

\begin{document}

\begin{align*}
  \int_{0}^{\pi /2}f(x)dx
    &= \int_{0}^{\pi /2} \sin ^{7}x \cos^{5}xdx \\
    &= \int_{0}^{\pi /2} \sin ^{7}x \cdot \cos xdx - 2\int_{0}^{\pi /2}\sin^{9}x \cdot \cos xdx \\
    &\quad +\int_{0}^{\pi /2}\sin ^{11}x\cdot \cos xdx \\
    &= \frac{1}{8} - 2\cdot \frac{1}{10} + \frac{1}{12} \\
    &= \frac{1}{120}.
\end{align*}

\end{document}

I would also recommend to take a look at mathmode, a document by Herbert Voß which explains many details about math mode and the various environments available.

Regards