6. Inequalities in Two Triangles
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Add BC to both sides of the given inequality and use the Segment Addition Postulate. Next, apply the Converse of the Hinge Theorem.
Statements
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Reasons
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1. AB> CD
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1. Given
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2. AB +BC > CD + BC
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2. Adding BC to both sides
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3. AC = AB +BC and BD = CD + BC
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3. Segment Addition Postulate
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4. AC > BD
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4. Substitution
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5. AF≅ DJ and FC≅ JB
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5. Given
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6. m∠ AFC > m∠ DJB
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6. Converse of the Hinge Theorem
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Let's highlight the congruent segments AF≅ DJ and FC≅ JB in the diagram.
We are told that AB > DC. Then, by adding BC to both sides we get AB + BC > BC+ DC, and by the Segment Addition Postulate we obtain AC > BD. AF≅ DJ FC≅ JB AC > BD Finally, by the Converse of the Hinge Theorem we get that m∠ AFC > m∠ DJB, which is what we wanted to prove.
In the following table we will summarize the proof we did above.
Statements
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Reasons
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1. AB> CD
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1. Given
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2. AB +BC > CD + BC
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2. Adding BC to both sides
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3. AC = AB +BC and BD = CD + BC
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3. Segment Addition Postulate
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4. AC > BD
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4. Substitution
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5. AF≅ DJ and FC≅ JB
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5. Given
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6. m∠ AFC > m∠ DJB
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6. Converse of the Hinge Theorem
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