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Learn how to identify and use theorems to determine if a quadrilateral is a parallelogram in architectural structures, with examples and guided practice.
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ARCHITECTURE In the photograph, ST UVand ST UV. By Theorem 8.9, quadrilateral STUVis a parallelogram. EXAMPLE 2 Identify a parallelogram The doorway shown is part of a building in England. Over time, the building has leaned sideways. Explain how you know that SV =TU. SOLUTION By Theorem 8.3, you know that opposite sides of a parallelogram are congruent. So, SV = TU.
For what value of xis quadrilateral CDEFa parallelogram? ALGEBRA By Theorem 8.10, if the diagonals of CDEFbisect each other, then it is a parallelogram. You are given that CNEN. Find xso that FN DN. EXAMPLE 3 Use algebra with parallelograms SOLUTION
ANSWER Quadrilateral CDEF is a parallelogram when x = 4. EXAMPLE 3 Use algebra with parallelograms DN FN = Set the segment lengths equal. 3x 5x – 8 = Substitute 5x –8 for FN and 3xfor DN. 0 2x – 8 = Subtract 3xfrom each side. 8 2x = Add 8 to each side. 4 x = Divide each side by 2. FN = 5(4) –8 = 12 andDN = 3(4) = 12. Whenx = 4,
2. ANSWER Theorem 8.9 for Examples 2 and 3 GUIDED PRACTICE What theorem can you use to show that the quadrilateral is a parallelogram?
3. ANSWER Theorem 8.7 for Examples 2 and 3 GUIDED PRACTICE What theorem can you use to show that the quadrilateral is a parallelogram?
What theorem can you use to show that the quadrilateral is a parallelogram? 4. ANSWER Theorem 8.8 for Examples 2 and 3 GUIDED PRACTICE
5. For what value of xis quadrilateral MNPQa parallelogram? Explain your reasoning. 2; The diagonals of a parallelogram bisect each other so solve 2x = 10 – 3x forx. ANSWER for Examples 2 and 3 GUIDED PRACTICE