Angles & Lines
Grades 6–8 Geometry Angles
An angle is how much one ray turns away from another, measured in degrees. A full turn is 360°, half a turn is 180°.
- Acute — less than 90°
- Right — exactly 90° (marked with a small square)
- Obtuse — between 90° and 180°
- Straight — exactly 180°, a flat line
Pairs that add up
- Complementary — two angles summing to 90° (35° + 55°)
- Supplementary — summing to 180° (110° + 70°)
- Vertical — opposite angles when two lines cross: always equal
Parallel lines cut by a transversal
When a line slices two parallel lines, matching corners (corresponding angles) are equal — so once you know one angle in the pattern, you know all eight.
Watch out
Complementary angles don't need to touch. Any two angles summing
to 90° are complementary, wherever they live on the page.
Practice
The complement of 35° is ___°
The supplement of 110° is ___°
An angle of 127° is:
Two lines cross; one angle is 65°. Its vertical angle is ___°
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