**Symmetry Lines of a Rectangle**
A rectangle is a four-sided polygon with opposite sides equal in length and opposite angles equal in measure. When considering the concept of symmetry in geometry, it refers to the property of an object or shape that remains unchanged when certain transformations, such as reflection, rotation, or translation, are applied. In the case of a rectangle, there are several symmetry lines that can be identified.

**Definition of Symmetry Line**
A symmetry line, also known as a line of symmetry or axis of symmetry, is a line that divides a shape into two congruent halves, such that if one half is folded along the line, it perfectly overlaps the other half. In the case of a rectangle, these lines are determined by the arrangement of its sides and angles.

**Vertical Symmetry Line**
A rectangle has a vertical symmetry line passing through the midpoint of its length. This line divides the rectangle into two congruent halves, where each half is a mirror image of the other. If the rectangle is folded along this line, the two halves will perfectly overlap.

**Horizontal Symmetry Line**
Similarly, a rectangle also possesses a horizontal symmetry line passing through the midpoint of its width. This line divides the rectangle into two congruent halves, with each half being a mirror image of the other. Folding the rectangle along this line will result in perfect overlap between the two halves.

**Diagonal Symmetry Lines**
In addition to the vertical and horizontal symmetry lines, a rectangle also has two diagonal symmetry lines. These lines connect opposite corners of the rectangle, forming an X-shaped pattern. Folding the rectangle along any of these diagonal lines will create congruent halves, where each half reflects the other.

**Summary**
In conclusion, a rectangle has a total of four symmetry lines: one vertical, one horizontal, and two diagonal lines. These lines divide the rectangle into congruent halves, allowing for perfect overlap if folded along the symmetry line. Understanding the symmetry lines of a rectangle is essential in various mathematical and geometrical applications, as symmetry plays a significant role in analyzing and classifying shapes.

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