Mathematics — first biennium · Lesson
An isosceles-triangle property can be justified by comparing two internal triangles and applying a congruence criterion.
In this lesson: Use the isosceles property and its converse and complete simple proof steps through congruence.
How to proceed: Count the given data: two corresponding sides and the included angle are congruent. Only after proving congruence may you deduce equality of corresponding parts.
You can already assume: Triangle congruence criteria.
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Count the given data: two corresponding sides and the included angle are congruent. Only after proving congruence may you deduce equality of corresponding parts.
Given data: ABC is isosceles with AB=AC. AD bisects ∠A, so ∠BAD=∠DAC; AD is also common to triangles ABD and ACD.
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Relationships: solid line = required · dashed line = recommended · dotted line = reinforcement.