Similar Triangles and Polygons Practice Problems

Master similarity ratios, scale factors, and proportional relationships with step-by-step practice problems for similar triangles and polygons

📚Master Similar Triangles and Polygons with Interactive Practice
  • Calculate scale factors and similarity ratios between corresponding sides
  • Identify corresponding angles and sides in similar triangles
  • Solve for missing side lengths using proportional relationships
  • Apply AA, SAS, and SSS similarity theorems to prove triangles similar
  • Find areas and perimeters of similar polygons using scale factors
  • Use similar triangles to solve real-world measurement problems

Understanding Similar Triangles and Polygons

Complete explanation with examples

Similarity of triangles and polygons

Similar triangles are triangles whose three angles are equal respectively and also the ratio between each pair of corresponding sides is equal. Two similar triangles are actually larger or smaller versions each other.

The ratio of similarity is the ratio between two corresponding sides in two similar triangles.

To prove similarities between triangles, we will use the following theorems:

  • Angle-Angle (A.A): If two angles are equal respectively between two triangles, then the triangles are similar.
  • Side-Angle-Side (S.A.S): If the ratio of two pairs of sides is equal, and also the angles between them are equal to each other, then the triangles are similar.
  • Side-Side-Side (S.S.S.): If for two triangles, the ratio of the three sides in one triangle to the three pairs in the other triangle is equal (similarity ratio), then the triangles are similar.

For similarity of polygons we will define it this way: if for two polygons all angles are equal and there is a constant ratio between two corresponding sides, then the polygons are similar.

Intuitively, just like similar triangles, also two similar polygons are actually an enlargement or reduction of each other.

Image 1 similar triangles

Detailed explanation

Practice Similar Triangles and Polygons

Test your knowledge with 42 quizzes

AAADDDFFFBBBCCC65°40°40°Which of the following are true?

Examples with solutions for Similar Triangles and Polygons

Step-by-step solutions included
Exercise #1

10062.5508080100 Are the two triangles similar?

Step-by-Step Solution

To find out if the triangles are similar, we can check if there is an appropriate similarity ratio between their sides.

The similarity ratio is the constant difference between the corresponding sides.

 

In this case, we can check if:

62.550=10080=10080 \frac{62.5}{50}=\frac{100}{80}=\frac{100}{80}

62.550=125100=125100=114 \frac{62.5}{50}=\frac{125}{100}=1\frac{25}{100}=1\frac{1}{4}

10080=108=124=114 \frac{100}{80}=\frac{10}{8}=1\frac{2}{4}=1\frac{1}{4}

 Therefore:114=114=114 1\frac{1}{4}=1\frac{1}{4}=1\frac{1}{4}

Therefore, we can say that there is a constant ratio of114 1\frac{1}{4} between the sides of the triangles and therefore the triangles are similar.

Answer:

Yes

Video Solution
Exercise #2

AAABBBCCCDDDEEE60°30°30°60°ΔACBΔBED ΔACB∼ΔBED

Choose the correct answer.

Step-by-Step Solution

First, let's look at angles C and E, which are equal to 30 degrees.

Angle C is opposite side AB and angle E is opposite side BD.

ABDB \frac{AB}{DB}

Now let's look at angle B, which is equal to 90 degrees in both triangles.

In triangle ABC the opposite side is AC and in triangle EBD the opposite side is ED.

ACED \frac{AC}{ED}

Let's look at angles A and D, which are equal to 60 degrees.

Angle A is the opposite side of CB, angle D is the opposite side of EB

CBEB \frac{CB}{EB}

Therefore, from this it can be deduced that:

ABBD=ACED \frac{AB}{BD}=\frac{AC}{ED}

And also:

CBED=ABBD \frac{CB}{ED}=\frac{AB}{BD}

Answer:

Answers a + b are correct.

Video Solution
Exercise #3

AAABBBCCCMMMNNN36 What is the ratio between the sides of the triangles ΔABC and ΔMNA?

Step-by-Step Solution

From the data in the drawing, it seems that angle M is equal to angle B

Also, angle A is an angle shared by both triangles ABC and AMN

That is, triangles ABC and AMN are similar respectively according to the angle-angle theorem.

According to the letters, the sides that are equal to each other are:

ABAM=BCMN=ACAN \frac{AB}{AM}=\frac{BC}{MN}=\frac{AC}{AN}

Now we can calculate the ratio between the sides of the given triangles:

MN=3,BC=6 MN=3,BC=6 63=2 \frac{6}{3}=2

Answer:

BCMN=2 \frac{BC}{MN}=2

Video Solution
Exercise #4

Is the similarity ratio between the three triangles equal to one?

Step-by-Step Solution

To answer the question, we first need to understand what "similarity ratio" means.

In similar triangles, the ratio between the sides is constant.

In the statement, we do not have data on any of the sides.

However, a similarity ratio of 1 means that the sides are exactly the same size.

That is, the triangles are not only similar but also congruent.

In the drawing, you can clearly see that the triangles are of different sizes and, therefore, clearly the similarity ratio between them is not 1.

Answer:

No

Exercise #5

1027.51.5The two parallelograms above are similar. The ratio between their sides is 3:4.

What is the ratio between the the areas of the parallelograms?

Step-by-Step Solution

The square of the ratio between the sides is equal to the ratio between the areas of the parallelograms:

32:42=9:16 3^2:4^2=9:16

Answer:

9:16

Video Solution

Frequently Asked Questions

How do you find the scale factor between two similar triangles?

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To find the scale factor, divide the length of any side in the larger triangle by the corresponding side in the smaller triangle. For example, if corresponding sides are 12 and 8, the scale factor is 12/8 = 1.5.

What are the three ways to prove triangles are similar?

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The three similarity theorems are: 1) AA (Angle-Angle) - two angles are equal, 2) SAS (Side-Angle-Side) - two sides are proportional with included angles equal, 3) SSS (Side-Side-Side) - all three sides are proportional.

How do you find missing sides in similar triangles?

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Set up a proportion using corresponding sides. If triangles ABC and DEF are similar, then AB/DE = BC/EF = AC/DF. Cross multiply to solve for the unknown side length.

What is the difference between congruent and similar triangles?

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Congruent triangles have identical size and shape (all corresponding sides and angles are equal). Similar triangles have the same shape but different sizes (corresponding angles are equal, but sides are proportional).

How do you calculate the area ratio of similar polygons?

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The area ratio equals the square of the scale factor. If the scale factor is 3:2, then the area ratio is 3²:2² = 9:4. This means the larger polygon has 9/4 times the area of the smaller one.

What are corresponding parts in similar triangles?

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Corresponding parts are sides and angles that occupy the same relative position in similar triangles. Corresponding angles are always equal, while corresponding sides are proportional (have the same ratio).

How do you solve real-world problems using similar triangles?

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Identify the similar triangles in the problem, set up proportions using known and unknown measurements, then solve for the missing value. Common applications include shadow problems, map scaling, and indirect measurement.

Why are all circles similar to each other?

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All circles are similar because they have the same shape - every circle can be transformed into any other circle through scaling (changing size) and translation (changing position). The ratio of circumference to diameter (π) is constant for all circles.

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