# Objective

is to represent equation array using LaTeX.

## Example 1.

### Code

\$$\\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\\} \$$

### Result

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

## Example 2.

### code

\$$\\begin{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} \$$

### Result

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

## References

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