how do we use a set square in construvtions?

### Drawing Parallel Lines

A ruler and set square can be used to draw parallel lines as described below.

**Step 1:** Position an edge of the set square against a ruler and draw a line along one of the other edges.**Step 2:** Slide the set square into a new position while keeping the ruler fixed exactly at the same position.**Step 3:** Draw a line along the same edge that was used in Step 1.

Example 17

Use a ruler and set square to draw a line that is parallel to a given line, *AB*, and passes through a given point, *P*.

##### Solution:

**Step 1:** Position an edge of the set square along the given line, *AB*.**Step 2: **Place a ruler** **against one of the other edges.**Step 3:** Slide the set square along the ruler until the edge used in Step 1 passes through the given point *P*.**Step 4:** Draw the line *CD *through *P*.

The line *CD* passes through the given point, *P*, and is parallel to the given line* AB*.

Perpendicular Lines

Lines that are at right angles to each other are said to be **perpendicular lines**.

Note that a **vertical line** is perpendicular to the **horizontal**, whereas **perpendicular lines** can be drawn in any position. Bricklayers use a plumb-bob to set out vertical lines and a spirit level to set out horizontal lines.

Drawing Perpendicular Lines

A set square can be used to draw a perpendicular at a point on a given line as described below.

**Step 1:** Set an edge of the set square on the given line so that the other edge is just in contact with the point.**Step 2:** Draw a line that passes through the given point with the help of the set square.

Example 18

Use a set square to draw a perpendicular to a given line, *AB*, through a point, *P*, not on the line.

##### Solution:

**Step 1:** Set an edge of the set square on the given line so that the other edge is just in contact with the point.**Step 2:** Draw a line that passes through the given point with the help of the set square.