Angles and triangles
Angles on a straight line, around a point, vertically opposite angles and the 180° of a triangle. Read one step, play with it, then tap “I understand this”.
Angles on a straight line
A straight line is a half turn: 180°. Angles that lie together on a straight line add up to 180°.
The straight line
Change angle a and watch b.
Angles around a point
Around a point is a full turn: 360°. If you add all the angles around a point, you always get 360°.
Four right angles around a point: 4 × 90° = 360°.
Vertically opposite angles
When two straight lines cross, the angles opposite each other are equal.
Crossing lines
Change angle a.
a + b = 180°, because they lie on a straight line. The opposite angle + b = 180° too. So both are 180° − b, and that is why they must be equal.
The angles of a triangle
The three angles of any triangle add up to 180°. If you know two angles, you can work out the third.
The triangle builder
Change angles A and B. The red angle is worked out.
Tear the three corners off a paper triangle and put them side by side: they make exactly a straight line!
Find the missing angle
Which angle is missing?
Use 180° or 360°.
Correct: 0Check yourself
- Angles on a straight line: 180°.
- Angles around a point: 360°.
- Vertically opposite angles are equal.
- The angles of a triangle: 180°.
- Equilateral: 3 equal sides. Isosceles: 2. Scalene: none.
Write these points in your maths book. Read them again the night before the test.
Quick questions
Tap an answer. If you get one wrong, read why and go back to that step. You get new questions every time.
You ticked all 5 steps! Now you are ready for the quiz.- Practice sheet for this classQuestions + memo · 2 A4 pagesPractice sheet
- Geometry8 pages · PDFPaperMemo
- Space and shape10 pages · PDFPaperMemo
Ready for more? The Grade 7 geometry quiz gives you new questions every time.
- One step a day is enough. Ten calm minutes work better than an hour the night before the test.
- Do the paper triangle experiment together (step 4): it is the best way to remember that a triangle’s angles make 180°.
- Ask your child to tell you the rule in their own words. If they can explain it, they understand it.
- The ticks (“I understand this”) are saved on this device only. We never ask for names or emails.
Follows CAPS for Grade 7 Maths. Always check your teacher’s notes and textbook too.