Geometry of Straight Lines: Angle Relationships

Study Notes

A full revolution is 360°, and a half revolution is 180°.
When two angles on a straight line sum to 180°, they are called supplementary angles.
Angles on a straight line always sum to 180°.
Supplementary angles are two angles whose sum is 180°.
Perpendicular lines intersect to form equal angles of 90°.
When two lines intersect, the vertically opposite angles are equal.
When a line forms two equal angles where it meets another line, these lines are perpendicular.

When a line forms two equal angles where it meets another line, these lines are perpendicular.
Each angle in this case is 90° because the sum of the angles on a straight line is 180°.

A transversal is a line that intersects two or more other lines.
When a transversal intersects parallel lines, the corresponding angles are equal.
Alternate angles are equal when the lines are parallel.
Co-interior angles are angles on the same side of the transversal and inside the two intersected lines.
The sum of co-interior angles is 180°.

Identify the lines and angles formed by the intersection of lines.
Measure angles using a protractor to check their properties.
Determine relationships between angles using the properties of parallel lines and transversals.
Identify supplementary angles by checking angles on a straight line and verifying their sum is 180°.
Identify vertically opposite angles by checking when two lines intersect.
Identify corresponding angles by looking for angles in matching corners when a transversal intersects parallel lines.
Identify alternate angles by finding pairs of angles on opposite sides of the transversal and inside the parallel lines.
Identify co-interior angles by checking pairs of angles on the same side of the transversal and inside the parallel lines; their sum should be 180°.

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