Solids, flat shapes and position · Usually met around P1
Straight and curved lines
A straight line follows the ruler.
How to do it
Method
A straight line follows the ruler
Only one straight line joins two points
Another way
Check with a ruler
Follows the ruler all the way → straight
In full
A straight line has no bends; a curved line bends. To check whether a line is straight, hold a ruler beside it: a straight line follows the ruler all the way. To draw a straight line, join two points with a ruler: through two points you can draw only one straight line, and it is the shortest way between them. Joining points in a row one after another, there is one more point than there are lines.
Worked examples
Have a go first, then open each one for the answer and the working.
Example 1
How many straight lines are in the picture?
Show the answer and working
Answer: 2 lines
Look at each: straight or bending. There are 2 straight lines.
Example 2
Through the two points 🖍️ and 🚗, you can draw exactly 1 straight line(s).
True or false?
Show the answer and working
Answer: True
Join two points with a ruler: only one straight line goes through both.
Example 3
Tsz-hin marks 10 points along a line and joins each pair of neighbouring points with a ruler. How many short straight lines does Tsz-hin draw?
Show the answer and working
Answer: 9 lines
One line between each pair of neighbours: one fewer line than points, 10 − 1 = 9.
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