#### Reflection

- When an object (P) is placed before a plane mirror, the image formed is at the same distance (P’) behind the mirror as the object is in front of it.
- The line l is the perpendicular bisector of PP’ and is also called the mirror line or mediator

#### The two perpendicular lines (co-ordinate axes)

- The horizontal line X’X is called the x-axis.
- The vertical line Y’Y is called the y-axis.
- The point where X’X and Y’Y intersect is called the origin and is denoted by O.
- The directions OX and OY are called the positive directions of the x-axis and y-axis, respectively.
- The directions OX’ and OY’ are called the negative directions of the x-axis and y-axis, respectively.
- The two axis together are called the axes.

#### Reflection of a point P

- In the line y = 0 i.e. in the x-axis
- The mirror image of the point P (a, b) is P’ (a, -b)
- The sign of its ordinate changes

- In the line x = 0 i.e. in the y-axis
- The mirror image of the point P (a, b) is P’’ (-a, b)
- The sign of its abscissa changes

- In the origin

1. The mirror image of the point P (a, b) is

P’’’ (-a, -b)

2. The sign of its ordinate and abscissa changes

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