Big Ideas Math Geometry, 2014
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Big Ideas Math Geometry, 2014 View details
5. Properties of Trapezoids and Kites
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Exercise 18 Page 403

Use the fact that the noncongruent adjacent sides of a kite form congruent angles.

m∠ G=70^(∘)

Practice makes perfect

We are given the following diagram and asked to find the measure of ∠ G.

We can see that the quadrilateral has two pairs of consecutive congruent sides, but its opposite sides are not congruent. This means HEFG is a kite, so we can use the Kite Opposite Angles Theorem.

Kite Opposite Angles Theorem

If a quadrilateral is a kite, then exactly one pair of opposite angles are congruent.

The congruent angles of a kite are formed by the noncongruent adjacent sides. In our case, the noncongruent adjacent sides are EF and FG, and EH and HG. They form angles ∠ F and ∠ H, respectively. Therefore, ∠ F and ∠ H are congruent. ∠ H≅ ∠ F ⇒ m∠ H= m∠ F Since ∠ F is a right angle, it measures 90^(∘). This allows us to conclude that ∠ H also measures 90^(∘). m∠ H= 90^(∘) By the Corollary to the Polygon Interior Angles Theorem the sum of the measures of the interior angles of any quadrilateral is 360^(∘). Applying it to HEFG, we can form the following equation. m∠ H+ m∠ E+ m∠ F+m∠ G=360^(∘) Substituting 90^(∘) for m∠ H and m∠ F, and 110^(∘) for m∠ E, we will get an equation where the only unknown is m∠ G. Let's solve it!
90^(∘)+ 110^(∘)+ 90^(∘)+m∠ G=360^(∘)
290^(∘) +m∠ G=360^(∘)
m∠ G=70^(∘)
We conclude that the measure of ∠ G is 70^(∘).