Beyond Rankers Academy
Building Minds, Not Just Rankers
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Beyond Rankers Academy
Building Minds, Not Just Rankers
Main site →
Geometry rewards drawing. Almost every question here is solved by sketching the figure and marking what you know on it.
Angles are named by size, and pairs of angles are named by what they add to.
📐 Names by size and by pair
| Name | Meaning |
|---|---|
| Acute | less than 90° |
| Right | exactly 90° |
| Obtuse | between 90° and 180° |
| Straight | exactly 180° |
| Reflex | more than 180° |
| Complementary | a pair adding to 90° |
| Supplementary | a pair adding to 180° |
Do not swap these two. Complementary → Corner → 90°. Supplementary → Straight → 180°. The first letters match the picture.
When a line cuts two parallel lines, eight angles appear — but only two different sizes among them.
🛤️ Which pairs are equal
| Pair | Relationship |
|---|---|
| Corresponding | equal — they sit in matching corners (an F shape) |
| Alternate interior | equal — inside, on opposite sides (a Z shape) |
| Vertically opposite | equal — across an X |
| Co-interior | add to 180° (a C or U shape) |
Look for the letters. An F shape means corresponding angles (equal). A Z shape means alternate angles (equal). A C shape means co-interior angles (adding to 180°). Tracing the letter on the figure is faster than recalling the name.
A figure has line symmetry if it folds onto itself, and rotational symmetry if it looks the same after a turn.
🔷 Symmetry of common shapes
| Shape | Lines of symmetry | Order of rotation |
|---|---|---|
| Square | 4 | 4 |
| Rectangle | 2 | 2 |
| Equilateral triangle | 3 | 3 |
| Rhombus | 2 | 2 |
| Regular hexagon | 6 | 6 |
| Circle | infinite | infinite |
| Parallelogram | 0 | 2 |
A parallelogram has no line of symmetry — folding it never matches. But it does have rotational symmetry of order 2, because turning it half a turn gives the same shape. Line and rotational symmetry are different things.
12 questions on angles, lines and symmetry. Draw before you decide. 🍀