McGraw Hill Integrated II, 2012
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McGraw Hill Integrated II, 2012 View details
5. Isosceles and Equilateral Triangles
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Exercise 21 Page 379

x=11
y=11

Practice makes perfect

To find the values of the variables, the first thing we need to remember is the Triangle Angle-Sum Theorem.

Triangle Angle-Sum Theorem

The sum of the interior angles of a triangle is 180^(∘).

Using this theorem, we can write the following.

m∠ X+ m∠ Y+ m∠ W=180 ⇓ (6y-2)+(4x+20)+52=180 Now, by the given markings, we can see that WX≅WY.

By the Isosceles Triangle Theorem, we know that if two sides of a triangle are congruent, then the angles opposite those sides are congruent. With this theorem in mind, we can conclude that ∠ X ≅ ∠ Y and that their measures are equal. m∠ X =& m ∠ Y ⇓ 6y-2=& 4x+20 Knowing that these expressions are equal, we can substitute one for the other in our equation created by the Interior Angles Theorem. Let's first find the value of x.
(6y-2)+(4x+20)+52=180
( 4x+20)+(4x+20)+52=180
Solve for x
4x+20+4x+20+52=180
8x+92=180
8x=88
x=11
Finally, we can find the value of y by substituting x=11 into either known equation. For simplicity, we will use the equation relating the side lengths.
6y-2=4x+20
6y-2=4( 11)+20
Solve for y
6y-2=44+20
6y-2=64
6y=66
y=11