Lesson 0 of 16
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Show on a big screenTwo tiffin lids swap boxes. Each lid still closes the other box exactly.
What this track covers
Your textbook calls these figures Geometric Twins. The maths word is congruent. It means the same shape and the same size.
- Landing one shape on another. The test for twins.
- Slide, turn, flip. Three moves that change nothing.
- A bigger copy. It is not a twin.
- One line, one corner. The test on a single length or angle.
- Three sides (SSS). Enough to fix a triangle. Only one shape and size can be drawn.
- Two sides and the angle between (SAS). Also enough.
- Two angles and a side (ASA, AAS). Also enough.
- Three angles (AAA). Not enough.
- Writing it in order. ΔABC ≅ ΔXYZ, and which corners match.
- A right angle, the hypotenuse, a side (RHS). Also enough.
- Equal sides, equal angles. Two equal sides give two equal angles.
- Twins in a figure. Read the marks, then name the condition.
This is Chapter 1 of Part II, Geometric Twins.
Quick catch-up
- Fold and match, from symmetry.
- Turning a shape, from symmetry.
- Exact, not neat, from constructions.
- Measuring an angle, from lines and angles.