Geometry Angles Post 9

Angles on Parallel Lines
Parallel lines are lines that never cross because they are travelling in the same direction.  We use
arrows on the lines to represent parallel lines. 

railway lines never touch

Perpendicular lines cross at 90 degrees (not needed but interesting).

Parallel lines are particularly good at creating interesting math problems especially when they combine with our previous geometry rules (angles inside triangles, angles at a point, angles on a straight line or vertically opposite angles are equal). 

parallel lines

The main ways that angles can form on parallel lines is if we have a line that crosses over the parallel lines (a transversal).  Then we can form the three main types of angles on parallel lines...

1. Corresponding Angles (are equal),
2. Co-interior Angles (add to 180), and,
3. Alternative Angles (are equal).

Builders and architects especially need to be good with angles on parallel lines...



See all the parallel lines.
 

The work for angles on straight lines can be found on pages 253 - 272 Exercises 18.1 to 18.7. 




Can you see how each of the angles a, b, c, and d can be calculated using our geometry rules?