Ratios, Proportions and Similar Polygons

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Questions and Answers

A fruit bowl contains 5 apples and 7 oranges. What is the ratio of oranges to the total pieces of fruit?

  • 7:12 (correct)
  • 7:5
  • 5:7
  • 5:12

The sides of a triangle are in the extended ratio 3:5:8, and its perimeter is 48 cm. What is the length of the shortest side?

9

In the proportion 4/7 = 12/21, the means are 4 and 21.

False (B)

In a proportion, the product of the extremes equals the product of the ______.

<p>means</p> Signup and view all the answers

Solve for x in the following proportion: 3/x = 9/15

<p>5 (D)</p> Signup and view all the answers

What is the arithmetic mean of the numbers 4 and 16?

<p>10</p> Signup and view all the answers

What is the geometric mean of 5 and 20?

<p>10 (C)</p> Signup and view all the answers

If a/b = c/d, then a/d = c/b is a valid transformation according to the properties of proportions.

<p>False (B)</p> Signup and view all the answers

Given that x/y = 5/2, which of the following is equivalent based on the properties of proportions?

<p>(x+y)/y = 7/2 (B)</p> Signup and view all the answers

Two similar triangles have corresponding side lengths of 4 and 12. What is the scale factor of the smaller triangle to the larger triangle?

<p>1/3</p> Signup and view all the answers

If two polygons are congruent, what is their scale factor?

<p>1:1 (C)</p> Signup and view all the answers

If two triangles are similar, their corresponding angles are proportional.

<p>False (B)</p> Signup and view all the answers

If ΔPQR ~ ΔXYZ, then ∠P is congruent to ∠______.

<p>X</p> Signup and view all the answers

Given ΔABC ~ ΔDEF, AB = 8, DE = 12, and BC = 6, find the length of EF.

<p>9 (B)</p> Signup and view all the answers

ΔABC has angle measures ∠A = 50° and ∠B = 70°. ΔXYZ has angle measures ∠X = 50° and ∠Y = 70°. Are the triangles similar? If so, by which theorem?

<p>AA</p> Signup and view all the answers

What is the minimum amount of information needed to prove that two triangles are similar using Angle-Angle Similarity (AA~)?

<p>Two pairs of congruent angles. (B)</p> Signup and view all the answers

Side-Side-Angle (SSA) is a valid method for proving triangle similarity.

<p>False (B)</p> Signup and view all the answers

If two triangles have two pairs of sides whose lengths are in the same proportion, and the included angles are congruent, then the triangles are similar by ______ similarity.

<p>SAS</p> Signup and view all the answers

In ΔABC and ΔXYZ, AB/XY = BC/YZ = CA/ZX = 2. By which similarity postulate or theorem are the triangles similar?

<p>SSS~ (A)</p> Signup and view all the answers

Given ΔABC and ΔDEF, where AB = 4, BC = 6, DE = 6, EF = 9, and ∠B ≅ ∠E. Are the triangles similar? If so, by what theorem?

<p>SAS</p> Signup and view all the answers

If the geometric mean of two numbers is 6, and one of the numbers is 4, what is the other number?

<p>9 (C)</p> Signup and view all the answers

When an altitude is drawn to the hypotenuse of a right triangle, the two smaller triangles formed are similar to each other, but not similar to the original triangle.

<p>False (B)</p> Signup and view all the answers

In a right triangle, the altitude from the right angle to the hypotenuse divides the hypotenuse into two segments. The length of the altitude is the ______ mean of the lengths of the two segments.

<p>geometric</p> Signup and view all the answers

In a right triangle with the altitude drawn to the hypotenuse, if one segment of the hypotenuse is 4 and the other is 9, what is the length of the altitude?

<p>6 (C)</p> Signup and view all the answers

In a right triangle, the altitude to the hypotenuse divides the hypotenuse into segments of length 3 and 12. What is the length of the shorter leg of the original triangle?

<p>6</p> Signup and view all the answers

What transformation changes the size of a figure?

<p>Dilation (C)</p> Signup and view all the answers

A dilation with a scale factor of 0.7 is an enlargement.

<p>False (B)</p> Signup and view all the answers

To dilate a figure by a scale factor of k using the origin as the center of dilation, the transformation is (x, y) -> (______, ______).

<p>kx, ky</p> Signup and view all the answers

A triangle with vertices A(2, 4), B(6, 2), and C(4, 8) is dilated by a factor of 2. What are the coordinates of vertex A'?

<p>(4, 8) (A)</p> Signup and view all the answers

A square has a side length of 3 cm. It is enlarged to a square with a side length of 12 cm. What is the scale factor of the enlargement?

<p>4</p> Signup and view all the answers

Two similar figures have a scale factor of 5:3. What is the ratio of their areas?

<p>25:9 (B)</p> Signup and view all the answers

If two similar triangles have perimeters in the ratio of 2:3, then their areas are in the ratio of 4:9.

<p>True (A)</p> Signup and view all the answers

If the scale factor for the area of two polygons is 9:4, then the scale factor for their side lengths is ______.

<p>3:2</p> Signup and view all the answers

A 6m high pole casts a shadow of 4m. At the same time, a nearby tree casts a shadow of 12m. How high is the tree?

<p>18m (A)</p> Signup and view all the answers

You are creating a scale model of a building that is 50 feet tall. If you want your model to be 2 feet tall, what is the scale factor you should use?

<p>1/25</p> Signup and view all the answers

The Side-Splitter Theorem applies when a line intersects a triangle side at its midpoint.

<p>False (B)</p> Signup and view all the answers

The Side-Splitter Theorem states that if a line parallel to one side of a triangle intersects the other two sides, then it divides the two sides ______.

<p>proportionally</p> Signup and view all the answers

In ΔABC, DE is parallel to BC, AD = 4, DB = 6, and AE = 5. Find EC.

<p>7.5 (A)</p> Signup and view all the answers

Three parallel lines intersect two transversals. The segments on one transversal are 6 and 9, and the corresponding segment on the second transversal adjacent to the '6' segment is 4. What is the corresponding segment on the second transversal to the '9' segment?

<p>6</p> Signup and view all the answers

If a ray bisects an angle of a triangle, what relationship is established?

<p>It divides the opposite side into segments proportional to the other two sides. (A)</p> Signup and view all the answers

If a ray bisects an angle of a triangle, it always divides the opposite side into two equal segments.

<p>False (B)</p> Signup and view all the answers

If a ray bisects an angle of a triangle, then it divides the opposite side into segments whose lengths are ______ to the lengths of the other two sides.

<p>proportional</p> Signup and view all the answers

In ΔPQR, PS bisects ∠P, QS = 3, SR = 5, and PQ = 6. Find PR.

<p>10 (D)</p> Signup and view all the answers

Flashcards

Ratio

A comparison of two or more quantities; order matters.

Extended Ratio

A comparison of three or more quantities.

Proportion

An equation stating that two ratios are equal.

Extremes

The first and last numbers in a proportion.

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Means

The middle two numbers in a proportion.

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Cross Multiplication

The product of the extremes equals the product of the means.

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Arithmetic Mean

The average of a set of numbers.

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Geometric Mean

The positive value of x when a/x = x/b

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Similar Polygons

Figures where corresponding angles are congruent and corresponding sides are proportional.

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Scale Factor

The ratio of corresponding sides of similar polygons.

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Angle-Angle Similarity (AA~)

If two triangles have two pairs of congruent angles, then the two triangles are similar.

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Side-Angle-Side Similarity (SAS~)

If two triangles have two pairs of sides whose lengths are in the same proportion, and the included angles of the triangles are congruent, then the two triangles are similar.

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Side-Side-Side Similarity (SSS~)

If two triangles have three pairs of sides whose lengths are in the same proportion, then the two triangles are similar.

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Dilation

A transformation that changes the size of a figure proportionally.

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Scale Factor (k)

The constant by which each side length is multiplied by to create the image in a dilation.

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Enlargement

Has a scale factor greater than 1.

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Reduction

Has a scale factor less than 1.

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Perimeter Scale Factor

If the side lengths of two similar figures have a scale factor of a:b, then the perimeters have a scale factor of a:b.

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Area Scale Factor

If the side lengths of two similar figures have a scale factor of a:b, then the areas have a scale factor of a^2:b^2.

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Side Splitter Theorem

If a line parallel to one side of a triangle intersects the other two sides, then it divides the two sides proportionally.

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Parallel Lines and Transversals Theorem

If three parallel lines intersect two transversals, then the parallel lines divide the transversals proportionally.

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Angle Bisector Theorem

If a ray bisects an angle of a triangle, then it divides the opposite side into segments proportional to the other two sides.

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Study Notes

Ratios and Proportions

  • A ratio compares two or more quantities; order is important.
  • Ratios can be written as fractions (a/b) or with a colon (a:b).
  • An extended ratio compares three or more quantities.
  • A proportion is an equation stating that two ratios are equal.
  • In a proportion, the product of the extremes (first and last terms) equals the product of the means (middle terms); cross multiplication.
  • The arithmetic mean is the average of a set of numbers.
  • The geometric mean of two positive numbers a and b is x, where a/x = x/b.

Properties of Proportions

  • If a/b = c/d, then b/a = d/c (Flip).
  • Consequence: ad = bc.
  • If a/b = c/d, then a/c = b/d (Switch means/extremes).
  • Consequence: ad = bc.
  • If a/b = c/d, then (a+b)/b = (c+d)/d (Add denominator).
  • Consequence: a/b + 1 = c/d +1

Similar Polygons/Triangles

  • Congruent triangles have congruent corresponding angles and sides.
  • Similar polygons have congruent corresponding angles and proportional corresponding sides.
  • The scale factor is the ratio of corresponding sides in similar polygons.
  • Similarity statements are written with vertices in corresponding order.
  • Congruent figures are also similar with a scale factor of 1:1.

Triangle Similarity Theorems

  • Angle-Angle Similarity (AA~): Two triangles are similar if they have two pairs of congruent angles.
  • If two angles of one triangle are congruent to two angles of another triangle, then the triangles are similar.
  • Side-Angle-Side Similarity (SAS~): Two triangles are similar if they have two pairs of sides with proportional lengths and the included angles are congruent.
  • If two sides of one triangle are proportional to two sides of another triangle, and the included angles are congruent, then the triangles are similar.
  • Side-Side-Side Similarity (SSS~): Two triangles are similar if all three pairs of corresponding sides are proportional.
  • If all three sides of one triangle are proportional to the corresponding sides of another triangle, then the triangles are similar.

Geometric Mean Theorems

  • In a right triangle, the altitude from the right angle to the hypotenuse creates two smaller right triangles that are similar to each other and to the original triangle.
  • The altitude's length is the geometric mean of the two segments it creates on the hypotenuse.
  • The length of each leg of the original right triangle is the geometric mean of the length of the hypotenuse and the segment of the hypotenuse adjacent to that leg.

Dilations

  • A dilation enlarges or reduces a figure proportionally by a scale factor.
  • The scale factor (k) is the constant by which each side length or coordinate is multiplied.
  • Enlargements: k > 1
  • Reductions: 0 < k < 1
  • k = new side length/old side length.
  • To dilate a figure with the origin as the center: (x, y) -> (kx, ky).

Perimeters and Areas of Similar Figures

  • If two similar figures have a side length scale factor of a:b, then:
  • Their perimeters have a scale factor of a:b.
  • Their areas have a scale factor of a^2:b^2.

Applications of Similar Figures

  • Maps and blueprints
  • Animation and gaming
  • Scale models

Side Splitter Theorem

  • If a line is parallel to one side of a triangle and intersects the other two sides, it divides those sides proportionally.

Parallel Lines and Transversals Theorem

  • If three parallel lines intersect two transversals, they divide the transversals proportionally.

Triangle Angle Bisector Theorem

  • If a ray bisects an angle of a triangle, it divides the opposite side into segments proportional to the lengths of the other two sides.

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