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- communicate and justify fill in the missing reasons in the proof of theorem 5-9. (hint: the comparison property of inequality states that if a = b + c and c > 0, then a > b.)
given: ab > ac, \\(\overline{ac} \cong \overline{am}\\)
prove: \\(m\angle acb > m\angle b\\)
triangle diagram with points a, b, c, m and angles 1, 2, 3
statements | reasons
--- | ---
- \\(\overline{ac} \cong \overline{am}\\) | 1) given
- \\(m\angle 1 = m\angle 2\\) | 2) isosc. triangle thm.
- \\(m\angle acb = m\angle 2 + m\angle 3\\) | 3)
- \\(m\angle acb > m\angle 2\\) | 4)
- \\(m\angle acb > m\angle 1\\) | 5)
- \\(m\angle 1 = m\angle b + m\angle 3\\) | 6) ext. angles thm.
- \\(m\angle 1 > m\angle b\\) | 7)
- \\(m\angle acb > m\angle b\\) | 8)
- cor pro anc
15.
Step1: Angle Addition Postulate
The Angle Addition Postulate states that if a point lies in the interior of an angle, the measure of the whole angle is equal to the sum of the measures of the two smaller angles. So, for \(\angle ACB\), since \(m\angle ACB=m\angle2 + m\angle3\), the reason for statement 3 is the Angle Addition Postulate.
Step2: Comparison Property of Inequality
Given \(m\angle ACB=m\angle2 + m\angle3\) and \(m\angle3>0\) (because it is an angle measure), by the Comparison Property of Inequality (if \(a = b + c\) and \(c>0\), then \(a>b\)), we have \(m\angle ACB>m\angle2\). So the reason for statement 4 is the Comparison Property of Inequality.
Step3: Substitution
Since \(m\angle1 = m\angle2\) (from statement 2: Isosceles Triangle Theorem, which states that in an isosceles triangle, the base angles are equal. Here, \(\triangle ACM\) is isosceles with \(AC\cong AM\)), we can substitute \(m\angle2\) with \(m\angle1\) in the inequality \(m\angle ACB>m\angle2\). So the reason for statement 5 is Substitution.
Step4: Comparison Property of Inequality
Given \(m\angle1=m\angle B + m\angle3\) and \(m\angle3>0\) (because it is an angle measure), by the Comparison Property of Inequality (if \(a = b + c\) and \(c>0\), then \(a>b\)), we have \(m\angle1>m\angle B\). So the reason for statement 7 is the Comparison Property of Inequality.
Step5: Transitive Property of Inequality
We know that \(m\angle ACB>m\angle1\) (statement 5) and \(m\angle1>m\angle B\) (statement 7). By the Transitive Property of Inequality (if \(a > b\) and \(b>c\), then \(a>c\)), we have \(m\angle ACB>m\angle B\). So the reason for statement 8 is the Transitive Property of Inequality.
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- Angle Addition Postulate; 4) Comparison Property of Inequality; 5) Substitution; 7) Comparison Property of Inequality; 8) Transitive Property of Inequality.