McGraw Hill Integrated II, 2012
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McGraw Hill Integrated II, 2012 View details
6. Inequalities in Two Triangles
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Exercise 20 Page 459

Consider the Hinge Theorem.

7< x< 8.5

Practice makes perfect

For the given triangles, we will find the range of possible values for x. Let's start by labeling the vertices of the triangles.

In order to do that, we will use the Hinge Theorem to compare AB and CD. Therefore, we should find the measure of ∠ CAD. Notice that the sum of m∠ ACB and m∠ ACD is 90^(∘). 60+m∠ ACD=90 ⇒ m∠ ACD=30 From here, by the Triangle Angle Sum Theorem, we can find m∠ CAD.
m∠ CAD + m∠ ACD + m ∠ ADC = 180
m∠ CAD + 30 + 95 =180
m∠ CAD + 125 = 180
m∠ CAD = 55
Let's place these measures on the diagram.

Now, we are ready to use the theorem.

Applying the theorem, we can write an inequality for the side lengths. 60^(∘) > 55 ^(∘) ⇒ 5x+3 > 3x+17 Let's solve the inequality for x.
5x+3>3x+17
Solve for x
5x > 3x + 14
2x > 14
x > 7
All x-values greater than 7 will work. Besides that m∠ CAD is greater than m ∠ DCA. By the Triangle Larger Angle Theorem, the side opposite the larger angle is longer than the side opposite the lesser angle. 3x+17 > 5x Let's solve this inequality for x.
3x+17>5x
Solve for x
17>2x
8.5 > x
x < 8.5
Therefore, 8.5 is the upper limit of x. We can determine the range of possible values of x by combining the two inequalities. Inequality I:&& 7 < & x Inequality II:&& & x< 8.5 Combined:&& 7<& x<8.5