Bearings, Scale Drawing, Constructions & Loci (Edexcel GCSE Maths)

True or False?

To convert from a real-life distance to a scale distance, you usually need to divide by the scale factor.

To convert from a scale length to a real length, multiply by the scale factor.

E.g. 3 × 20 000 = 60 000 cm (600 m).

To convert from a real length to a scale length, divide by the scale factor.

E.g. 15 ÷ 50 000 = 0.000 3 km (30 cm).

True.

It may be helpful to convert the scale to more suitable units when dealing with very small or large scales.

For example, if 1 cm on a map represents 25 000 cm in real life, it may be easier to convert the units and use 1 cm represents 250 m or 0.25 km.

The compass direction for a bearing of 270º is due west.

The bearing for the compass direction of due northeast is 045º.

Remember to include 3 figures in your bearing.

False.

Scales on scale drawings are often given as a description with units.

This is unlike maps, where the scales are often given as ratios without units.

After measuring a distance on a scale drawing, the next step to find the corresponding real-life distance is to multiply by the scale factor.

The equipment you may need to be able to construct a triangle is:

• A sharp pencil

• A ruler

• A protractor

• A pair of compasses

When constructing a triangle, it could be for any of the following cases:

• SSS - you are given the lengths of all three sides.

• SAS - you are given the lengths of two sides and the angle in between them (the included angle).

• ASA - you are given the size of two angles and the length of the side in between them (the included side).

To construct a triangle when told the lengths of three sides (SSS):

1. Draw the longest side using a ruler as a horizontal base.

2. Use compasses set to the length of the next side and draw an arc from the end of the base line.

3. Repeat this for the third side, drawing an arc from the other end of the base line, the same length as the third side.

4. The arcs should intersect. Join the intersection of the arcs to each end of the base line using a ruler.

To construct a triangle when told the lengths of two sides and the angle between them (SAS):

1. Draw the longest side using a ruler as a horizontal base.

2. Use a protractor to measure the given angle from one end of the base line and make a mark on the paper at this angle.

3. Use a ruler to draw the second given side length from the end of the base line through the mark you have just made.

4. Check the lengths and angles are all correct so far using a ruler and protractor.

5. Use a ruler to draw the remaining side, between the end of the base line and the end of the second given side.

To construct a triangle when told two angles, and the length of a side between them (ASA):

1. Use a ruler to draw the given length as a horizontal base.

2. Use a protractor to measure the first given angle from one end of the base line and make a mark on the paper at this angle.

3. Use a ruler to join the end of the horizontal base line to the mark you have just made, and extend the line further.

4. Repeat steps 2 & 3 for the second given angle, at the other end of the base line.

5. The lines should intersect, forming a triangle.

True.

You should leave all your working and construction lines on the page, and not rub any out.

A perpendicular bisector is a line that cuts another line exactly in half (bisects) and also crosses it at a right angle (perpendicular).

To construct a perpendicular bisector:

1. Set the distance between the point of the compasses and the pencil to be more than half the length of the line.

2. Place the point of the compasses on one end of the line and sketch an arc above and below the line.

3. Keeping your compasses set to the same distance, move the point of the compasses to the other end of the line and sketch an arc above and below it again.

4. The arcs should intersect each other both above and below the line, connect the points where the arcs intersect using a ruler.

True.

The shortest distance from a point to a line is a straight line, which meets the line at 90 degrees.

E.g. When finding the shortest distance between a boat and a coastline, construct a perpendicular line from the boat to the coastline.

To construct a perpendicular to a line, from a point:

1. Set the distance between the point of your compasses and the pencil to be greater than the distance between the point and the line.

2. Place the point of the compasses onto the point and draw an arc that intersects the line in two places.

3. Make sure that the distance between the point of the compasses and the pencil is greater than half the distance between the intersection points. Place the point of the compasses on a point of intersection, and sketch an arc above and below the line.

4. Keeping the distance between the point on the compasses and the pencil the same, do this again from the other point of intersection. These should intersect with the previous arcs.

5. Join the original point with the point where the arcs intersect.

An angle bisector is a line that cuts an angle exactly in half (bisect).

To construct an angle bisector:

1. Place the point of the compasses at the point of the angle and sketch an arc that intersects both of the lines that form the angle.

2. Set the distance between the point of your compasses and the pencil to be greater than half the distance between the intersection points. Place the point of the compasses on one of the points of intersection and sketch an arc.

3. Keeping the distance between the point of the compasses and the pencil the same, place the point of the compasses on the other point of intersection and sketch another arc, this should intersect the arc sketched in step 2.

4. Join the point of the angle to the point of intersection of the arcs with a ruler.

The shape that is formed by points that are a fixed distance from a point is a circle.

False.

A path where all points are equidistant from a straight line will not be a parallel line on its own.

A race track shape will be formed consisting of a parallel line on either side of the straight line and a semi-circle at either end of the line connecting the parallel lines.

To identify an area that is closer to one point than another, you must find the path where all points are equidistant from the original two points.

To do this, you need to construct a perpendicular bisector between the two original points.

All points along an angle bisector are equidistant from the two lines that form the angle.