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Similar Polygons. Two polygons are similar if and only if their corresponding angles are congruent and the measures of the corresponding sides are proportional. is read is similar to. The order of the vertices in similarity statement is the same as a congruency statement. ABCD EFGH. B. A. - PowerPoint PPT Presentation
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Similar Polygons
Two polygons are similar if and only if their corresponding angles are congruent and the measures of the corresponding sides are proportional.
is read is similar to
The order of the vertices in similarity statement is the same as a congruency statement.
ABCDEFGH
A B
CD
E
GH
F
Rectangle WXYZ is similar to rectangle PQRS with a scale factor of 1.5. If the length and width of rectangle PQRS are 10 meters and 4 meters, respectively, what are the length and width of rectangle WXYZ?
Write proportions for finding side measures. Let one long side of each WXYZ and PQRS be and one short side of each WXYZ and PQRS be
Answer:
Quadrilateral GCDE is similar to quadrilateral JKLM
with a scale factor of If two of the sides of GCDE
measure 7 inches and 14 inches, what are the
lengths of the corresponding sides of JKLM?
Answer: 5 in., 10 in.
The scale on the map of a city is inch equals 2
miles. On the map, the width of the city at its widest
point is inches. The city hosts a bicycle race
across town at its widest point. Tashawna bikes at
10 miles per hour. How long will it take her to
complete the race?
Explore Every equals 2 miles. The
distance across the city at its widest point is
Solve
Cross products
Divide each side by 0.25.
The distance across the city is 30 miles.
Plan Create a proportion relating the measurements to the scale to find the distance in miles. Then use the formula to find the time.
Divide each side by 10.
Answer: 3 hours
It would take Tashawna 3 hours to bike across town.
Examine To determine whether the answer is reasonable, reexamine the scale. If 0.25 inches 2 miles, then 4 inches 32 miles. The distance across the city is approximately 32 miles. At 10 miles per hour, the ride would take about 3 hours. The answer is reasonable.
An historic train ride is planned between two landmarks on the Lewis and Clark Trail. The scale on a map that includes the two landmarks is 3 centimeters = 125 miles. The distance between the two landmarks on the map is 1.5 centimeters. If the train travels at an average rate of 50 miles per hour, how long will the trip between the landmarks take?
Answer: 1.25 hours
Triangle Proportionality Theorem
If a line is parallel to one side of a triangle and intersects the other two sides in two distinct points, then it separates these sides into segments of proportional lengths.
Example
From the Triangle Proportionality Theorem,
In and Find SU.
S
Answer: 15.75
In and Find BY.
B
Converse of the Triangle Proportionality Theorem
If a line intersect two sides of a triangle and separates the sides into corresponding segments of proportional lengths, the line is parallel to the third side.
Example
In and Determine
whether Explain.
In and AZ = 32.
Determine whether Explain.
Answer: No; the segments are not in proportion since
X
Triangle Midsegment Theorem
Midsegment of a triangle – a segment whose endpoints are the midpoints of two sides of the triangle
Triangle Midsegments Theorem – A midsegmet of a triangle is parallel to one side of the triangle, and its length is one-half the length of that side.
Example
Triangle ABC has vertices A(–2, 2), B(2, 4,) and C(4, –4). is a midsegment of Find the coordinates ofD and E.
(-2, 2)
(2, 4)
(4, –4)
Triangle ABC has vertices A(–2, 2), B(2, 4) and C(4, –4).
is a midsegment of Verify that
(-2, 2)
(2, 4)
(4, –4)
Triangle ABC has vertices A(–2, 2), B(2, 4) and C(4, –4).
is a midsegment of Verify that
(-2, 2)
(2, 4)
(4, –4)
Triangle UXY has vertices U(–3, 1), X(3, 3), and Y(5, –7). is a midsegment of
a. Find the coordinates of W and Z.
b. Verify that
c. Verify that
Answer: W(0, 2), Z(1, –3)
Answer: Since the slope of and the slope of
Answer: Therefore,
Proportional Perimeters Theorem
If two triangles are similar, then the perimeters are proportianal to the measures of corresponding sides.
If and find the perimeter of
Let x represent the perimeter of The perimeter of
C
If and RX = 20, find the perimeter of
Answer:
R
Special Segments of Similar Triangles
If two triangles are similar, then the measures of the corresponding altitudes are proportional to the measures of the corresponding sides.
Example
If two triangles are similar, then the measures of the corresponding angle bisectors of the triangle are proportional to the measures of the corresponding sides.
Example
If two triangles are similar, then the measures of the corresponding medians are proportional to the measures of the corresponding sides.
Example
In the figure, is an altitude of and is an altitude of Find x ifand
K
Answer: 17.5
N
In the figure, is an altitude of and is an altitude of Find x if and
The drawing below illustrates the legs, of a table. The top of the legs are fastened so that AC measures 12 inches while the bottom of the legs open such that GE measures 36 inches. If BD measures 7 inches, what is the height h of the table?
Answer: 28 in.