Angles and Basic Geometry
See the shapes, not just the words. This reviewer uses simple diagrams to teach angle relationships and basic plane-geometry ideas in a Grade 6–7 friendly way.
Angles and Basic Geometry
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Basic ideas to keep in mind
Line segment = has two endpoints
Ray = starts at one point and goes on in one direction
Angle = formed by two rays with the same endpoint
Right angle = 90°
Straight angle = 180°
Full turn = 360°
Angles in a triangle = 180°
See the relationships
Six patterns you should recognize
1. Identify angle types
An angle measuring 35° is acute. An angle measuring 90° is a right angle. An angle measuring 135° is obtuse.
2. Complementary angles
x + 37 = 90Subtract 37 from 90.
3. Supplementary angles
x + 125 = 180Subtract 125 from 180.
4. Vertical angles
If one angle in an X-shaped intersection is 72°, the vertical angle across from it is also 72°.
5. Angles in a triangle
48 + 67 + x = 180Add 48 and 67 to get 115. Then 180 − 115 = 65.
6. Parallel and perpendicular lines
Parallel lines never meet. Perpendicular lines meet to form a right angle.
Which relationship is it?
Two angles form a straight line. One angle is 146°. What is the other angle?
- A straight line means the two angles are supplementary.
- Supplementary angles add to 180°.
- 180 − 146 = 34.
Watch out for these
Complementary = 90°. Supplementary = 180°.
Angles inside a triangle always total 180°.
Opposite angles in an X-shape are equal.
Use the given measurements and facts, not just how “big” the drawing looks.
Build the skill
These mix angle types, complementary, supplementary, vertical angles, triangle angles, and line relationships.
Can you spot the angle fact fast?
Five quick questions. Use the shortest valid idea.
Can you do it without hints?
Score 5/5 to verify this competency. If you miss one, a fresh set will be ready.
Still mixing up angle relationships?
Send Teacher Abi your result or the exact item that confused you. I can help you see which geometry fact to use first.
Message Teacher AbiChoose your next step
Next competency: Perimeter and Area
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