Parallel and Intersecting Lines
When two lines cross
Fold paper and draw lines to see what happens when two lines cross.
Take a square sheet of paper and fold it in different ways. Draw a pencil line along each crease. Now you have several lines on one sheet.
Pick any two. Do they meet? If they don't meet on the paper, would they meet if you made them longer, past the edges? Keep this question in mind: the whole chapter is about it.
Everything here happens on a plane surface: a flat surface like a table top, your paper, the blackboard or a notice board.
Quick reminder: a line segment has two ends; a ray starts at one point and goes on for ever in one direction, like a torch beam; a line goes on for ever in both directions.
When two lines meet at a point on a plane, we say they intersect. Around the crossing point four angles are formed. Call them a, b, c, d.
Can two straight lines cross at more than one point? No. If two straight lines shared two points, they would be the same line. So two lines cross at one point at most.
Draw two crossing lines and measure all four angles with a protractor. Do this for four pairs. What patterns do you notice? The next lesson explains them.
Practise this lesson
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