Matching parts decide congruence
Two triangles look alike on the page. Do they match?
The rule
Not always: the measurements decide, not how they look.
Two triangles are congruent when all matching parts are equal. Three pairs of equal sides are enough to show it.
A shape can be turned or flipped. Your eye sees that first. This can mislead you.
- A turned or flipped copy looks different. Its sides are the same. It fits exactly on the first.
- An enlarged copy looks alike. Its sides are bigger. It does not fit on the first.
| Pair | Sides | Congruent? |
|---|---|---|
| 6, 8, 10 and 10, 8, 6 | the same three lengths | Yes |
| 6, 8, 10 and 9, 12, 15 | every side differs | No |
Read the numbers, not how the triangles are turned. Are they congruent?
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