5. Parts of Similar Triangles
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Use the definition of angle bisector and the Angle-Angle (AA) Similarity Postulate.
Statements
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Reasons
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1. △ QTS ~ △ XWZ, TR and WY are angle bisectors
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1. Given
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2. m∠ RTQ = 1/2m∠ T m∠ YWX = 1/2m∠ W |
2. Definition of angle bisector
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3. ∠ T ≅ ∠ W
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3. Definition of similar triangles
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4. m∠ T = m∠ W
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4. Definition of congruent angles
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5. m∠ RTQ = 1/2m∠ T m∠ YWX = 1/2m∠ T |
5. Substitution
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6. m∠ RTQ = m∠ YWX
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6. Substitution
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7. ∠ RTQ ≅ ∠ YWX
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7. Definition of congruent angles
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8. ∠ Q ≅ ∠ X
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8. Definition of similar triangles
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9. △ TRQ ~ △ WYX
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9. AA Similarity Postulate
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10. TR/WY = QT/XW
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10. Definition of similar triangles
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Let △ QTS and △ XWZ be a pair of triangles such that they are similar. Also, let TR and WY be angle bisectors.
LHS * 1/2=RHS* 1/2
1/2m∠ T= m∠ RTQ, 1/2m∠ W= m∠ YWX
Then, △ TRQ ~ △ WYX because of the Angle-Angle (AA) Similarity Postulate. This leads us to set the required proportion. TR/WY = QT/XW ✓
Given: & △ QTS ~ △ XWZ, TR and WY & are angle bisectors Prove: & TRWY = QTXW We will summarize the proof we did above in the following two-column table.
Statements
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Reasons
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1. △ QTS ~ △ XWZ, TR and WY are angle bisectors
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1. Given
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2. m∠ RTQ = 1/2m∠ T m∠ YWX = 1/2m∠ W |
2. Definition of angle bisector
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3. ∠ T ≅ ∠ W
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3. Definition of similar triangles
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4. m∠ T = m∠ W
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4. Definition of congruent angles
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5. m∠ RTQ = 1/2m∠ T m∠ YWX = 1/2m∠ T |
5. Substitution
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6. m∠ RTQ = m∠ YWX
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6. Substitution
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7. ∠ RTQ ≅ ∠ YWX
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7. Definition of congruent angles
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8. ∠ Q ≅ ∠ X
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8. Definition of similar triangles
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9. △ TRQ ~ △ WYX
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9. AA Similarity Postulate
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10. TR/WY = QT/XW
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10. Definition of similar triangles
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