Equation array

Objective

is to represent equation array using LaTeX.

Example 1.

Code

\begin{equation}
\left. \begin{array}{lllll}
\lambda_{11} & = & \cos(x'_1,x_1) & = & \cos\theta \\
\lambda_{12} & = & \cos(x'_1,x_2) & = & \cos \bigg( \frac{\pi}{2} - \theta \bigg) = \sin\theta \\
\lambda_{21} & = & \cos(x'_2,x_1) & = & \cos \bigg( \frac{\pi}{2} + \theta \bigg) = - \sin\theta \\
\lambda_{22} & = & \cos(x'_2,x_2) & = & \cos\theta
\end{array} \right\}
\end{equation}

Result

\left. \begin{array}{lllll} \lambda_{11} & = & \cos(x'_1,x_1) & = & \cos\theta \\ \lambda_{12} & = & \cos(x'_1,x_2) & = & \cos \bigg( \frac{\pi}{2} - \theta \bigg) = \sin\theta \\ \lambda_{21} & = & \cos(x'_2,x_1) & = & \cos \bigg( \frac{\pi}{2} + \theta \bigg) = - \sin\theta \\ \lambda_{22} & = & \cos(x'_2,x_2) & = & \cos\theta \end{array} \right\} 

Example 2.

code

\begin{equation}
\begin{array}{rcl}
\vec{A} \cdot \vec{r} & = & A_1 x_1 + A_2 x_2 + A_3 x_3 \\
& = & A^2 \\
& = & A^2_1 + A^2_2 + A^2_3
\end{array}
\end{equation}

Result

\begin{array}{rcl}  \vec{A} \cdot \vec{r} & = & A_1 x_1 + A_2 x_2 + A_3 x_3 \\  & = & A^2 \\  & = & A^2_1 + A^2_2 + A^2_3  \end{array} 

References

http://study-astrophysics.com/marion-01-08/

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